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Engineering Encounters

Trap the Zhu Zhu!

Upper elementary students use an engineering design process to trap a moving Zhu Zhu pet

Mousetraps. Bear traps. Ant traps. How do trap designs differ? How are they similar? What do you need to know about the intended victim? Does the shape, behavior, and movement of the animal play a role in the design of the trap? The activity presented here is an engaging engineering challenge that has been conducted with third- through fifth-grade students in school classrooms and during after-school programs. This article describes the hands-on activity as appropriate for fifth graders that supports the Next Generation Science Standards. This challenge incorporates life science standards by providing students the opportunity to consider the anatomy and behavior of the animal in the trap design. The entire activity as presented can be completed in approximately an hour but can also be expanded over several days and done in smaller increments of time for a richer experience.

Introducing Animal Traps

Most young students have limited experience with animal traps. They likely visualize a mousetrap with a spring that snaps down and kills the mouse. However, there are many other types of traps available! We began by showing students a picture of the typical mousetrap and asking students questions to get them thinking about the design of the mousetrap. Do you think this trap would work well with other small animals, such as a chipmunk? Would this trap work for larger animals? What kind of trap might work for a large animal such as a wolf or a bear? What kind of trap might work best for a medium-size animal such as a squirrel or a raccoon? What type of trap might you need for an animal that doesn’t walk on four legs, such as a bird? What type of trap may keep the animal alive?

As students worked their way through these questions and discussed each animal trap feature in small groups of two to four, a variety of modern traps were revealed to them (Figure 1) and posted on the classroom board where they remained for the duration of the lesson (alternatively, students could have time and resources to research traps on their own). Students began to ask questions themselves, such as, “What would you do to trap a snake?” or “I saw a trap that dropped a net onto an animal, but would that work if the animal was really strong and could rip through it?” Through student-led discussions in small groups, with very little teacher guidance, students began to understand that the size, shape, and movement of an animal dictates the structure and size that the trap needs to ultimately take. Students used the lens of the crosscutting concept structure and function to consider the parts of a trap that would be necessary to catch different animals. For example, students recognized that for a small, fast, light animal (a bird, mouse, etc.), their trap needed to have a smaller opening and a speedy mechanism to shut over the animal once it entered the trap. Whereas for a slower, bigger, heavier animal (a bear, wolf, etc.), it would be important for their trap to have a large opening and to be sufficiently heavy so the animal couldn’t move it.

Figure 1
Modern traps designed for different animals.

Modern traps designed for different animals. Photos courtesy of the authors.

The Design Challenge

With students now having an idea of different trap styles and how they relate to animal size and motion, we presented them with the engineering challenge of the day. Their job was to design a trap for a moving Zhu Zhu PetTM (see! We chose to use a Zhu Zhu (aka ZhuZhu) because it is small (approximately 4–5 inches in length and 2 inches wide) and because of its movement pattern. The Zhu Zhu movement may appear random at first, but after repeated observations, the students notice a pattern. We discuss with students that engineers do not work in isolation. They may need to gather data from other scientists, in this case a behavioral biologist. Real engineers must be knowledgeable about the animal so that they can build a trap to hold it. We thus invited students to the testing area (see Figure 2) to observe the behavior of the Zhu Zhu over several runs. With repeated observations, students noticed that the Zhu Zhu moves straight for approximately 18 inches, then moves backwards for approximately 6 inches before changing directions and moving forward again. The students discovered that their trap would likely be most successful if placed in line with the first 18 inches. In addition, students discovered that the Zhu Zhu can move in reverse and thus, in addition to an entrance, their trap must also prevent the Zhu Zhu from exiting by that same route. During this initial Zhu Zhu observation period, the students also noted that the Zhu Zhu moved faster than they thought and that it had some real power when it pushed against the side of the testing area. They also noted the size and shape of the Zhu Zhu, that it had wheels, ears, and sometimes hair that could affect the trap size and structure.

For this activity, the criteria for a successful trap are as follows:


  • Contains or immobilizes the Zhu Zhu pet for at least 10 seconds
  • The trap must be free-standing (i.e., not taped down)
  • The trap must be placed at a distance greater than 16 inches from the Zhu Zhu starting release point




Figure 2
The testing area.

The testing area.

Teaching in a Socially Distant World

  • Encourage students to watch a video of how Zhu Zhu Pets™ move. There are many on YouTube.
  • Permit students to work in virtual breakout rooms to share ideas and collaborate.
  • Invite students to draw a design of their trap at home, with the hope of testing it in the classroom at a later date.
  • Students might be allowed to use simple items at their own homes to build a trap that could later be tested in the classroom.
  • Zhu Zhu toys are affordable and a classroom might consider purchasing a couple that would be sanitized and shared among students when picking up other materials at school. Students could then test their trap at home before returning the Zhu Zhu toy to school.

As with all engineering endeavors in actuality and in the classroom, the students were given constraints as follows:

  • A $10 budget
  • No hands may enter the testing area at any time during testing
  • Nothing may be dropped into the testing area
  • There is a one-minute testing time limit per group and if the Zhu Zhu is not immobile by one minute then their turn is over
  • A time limit of 25 minutes total to design and build the trap, if the entire lesson is allotted an hour

The constraint of a $10 budget supports applied mathematics literacy and aligns with Disciplinary Core Ideas ETS1 and ETS2. Simple and inexpensive materials were assigned a monetary value based on how helpful we, as teachers, appraised them. For fifth graders, we chose increments of $0.50 but with more or less advanced classes you might consider using different monetary increments. Using smaller increments of money helps students with real-world application of the Common Core math standard CCSS.MATH.CONTENT.5.NBT.B.7: “Add, subtract, multiply and divide decimals to hundredths, using concrete models or drawings and strategies based on place value, properties of operations, and/or the relationship between addition and subtraction; relate the strategy to a written method and explain the reasoning.” Our list of materials and costs are shared online (see NSTA Connection). If students asked, “Can we return a material if we don’t use it?”, then we would allow them to return it for a refund if the item was in the exact condition it had been at the start (it hadn’t been cut, bent, or in any way changed). We also allowed the use of child-safe scissors for free.

Before students purchased materials, they worked in groups (2–4 students per group) to draw a prototype of the trap design. We find this planning stage an invaluable part of the design process. It forces students to think ahead of time about which materials they need to build their trap and to encourage group members to collaborate. Drawing out a design “encourages students to attend to detail and allows design ideas to be shared visually with others” (DCI ETS1.B Developing Possible Solutions).

Before purchasing supplies, the students were asked to show a teacher a fully labeled drawing of their proposed trap design and have the budget sheet completed to demonstrate that they stayed within the $10 limit.

During the design process, students often discovered that the idea they had drawn on the paper wasn’t going to work. They improved their designs during multiple phases of the engineering process. In some cases, this involved small material changes and in others it involved a major redesign. For the former, we allowed students to exchange unused materials as noted above. For the latter we encouraged students to draw a new labeled diagram, but more often they just started to play with materials and build a new trap. We allowed this process, as many students learn best by doing.

Testing and Revisions

When the design and building time had ended, we invited all students to come to the testing area. Prior to testing, each group was asked to give a brief description of their trap design and how they expected it to work. The students then placed their trap in the testing arena and the Zhu Zhu was released. After one minute, or a successful trapping, testing was complete. In most cases the initial design failed with the Zhu Zhu never entering the trap, escaping the trap, or the trap falling apart. Far from being discouraged, students learned a great deal from their design failure and were eager to improve on their trap designs. Students also gave feedback to other groups about what they thought worked well and what hadn’t worked well with their particular design, thus benefiting from multiple sources of feedback to help with their own future modifications. We assured the students that real scientists and engineers are seldom successful on their first attempt at solving a challenge and that we admired their perseverance. Students were then allowed 10 more minutes to redesign their trap before testing again. Some groups made small changes to their design and other groups started from scratch. Sometimes, when we have taught this lesson, we have asked students to start with a completely new $10 budget (they didn’t keep any of their old materials) and other times we asked students to adhere to the $10 budget but they could re-use their initial materials or exchange the unused pieces for a refund. Both approaches had value and the specific approach used was dependent on the availability of materials. The first method allows students to design an entirely new trap after observing the benefits and disadvantages of other trap designs. The second method encourages slight alterations to their own original design.

Occasionally we had students disagree about a test outcome. In these ambiguous cases, we reminded students of the success criteria and encouraged group discussion. For example, in one case the trap accidentally made the Zhu Zhu tip to its side and thus made the animal immobile. As a class, we decided that we would consider that a success, as the Zhu Zhu couldn’t move for the required 10 seconds as per the stated criteria. In another case, the wheel of the Zhu Zhu got stuck in netting attached to the trap and the critter couldn’t move because the wheel was jammed. As a class, we again decided that this was considered a success because the Zhu Zhu was immobilized for 10 seconds as per the defined criteria.

We have been impressed with the great variety of traps that the students have designed (Figure 3). When students began to understand that the allotted materials weren’t going to allow them to replicate a bear claw trap or a mousetrap, they had to really think about what they could do with the available materials. Some groups elected to build traps that involved having the Zhu Zhu get caught in netting, some tried to make a heavy rock fall onto the Zhu Zhu, some tried to make a cage that would close after the Zhu Zhu entered it, and others built ramps that would force the Zhu Zhu to tip over and be immobilized. The creativity and cooperation we saw was admirable!


Our own work with students and prior reports by others have suggested that STEM activities enhance reasoning and problem-solving skills, promote creativity, enhance collaboration, provide experience-based learning, increase student engagement, and allow students to accept failure as a route to success (Lachapelle and Cunningham 2014; Moulding, Bybee, and Paulson 2015). In this challenge, students learned a great deal, even with such a compressed lesson. They actively engaged in an engineering design process, created diagrams to convey their proposed trap (an element of the science and engineering practice of developing and using models), considered how structure and function are related, worked within constraints as a group, and used their creativity to design and redesign an effective trap. Students often asked to take their traps home to share with their families as a sign of their pride in achieving their goals, usually after an initial failure that led them toward a better redesign!

Figure 3
Student Zhu Zhu traps.

Student Zhu Zhu traps.

Sandra Pearl ( and Elizabeth Bless ( are executive directors of the nonprofit organization Science & Engineering Education Development (SEED), Inc. in Plainville, Massachusetts.


Lachapelle, C.P., and C.M. Cunningham. 2014. Engineering in elementary schools. In Engineering in pre-college settings: Synthesizing research, policy, and practices, eds. S. Purzer, J. Strobel, and M. Cardella, 61–88. Lafayette, IN: Purdue University Press.

Moulding, B., R. Bybee, and N. Paulson. 2015. A vision and plan for science teaching and learning. Essential Teaching and Learning Publications.

Biology Engineering Interdisciplinary Elementary Grade 4 Grade 5

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