Test both shapes. Which is more stable? 

Transform your triangle into a three sided pyramid. 

Transform your square into a cube.
Test stability of tetrahedron and cube.
What is more stable?

Build two Tetrahedrons to craft a
structure that looks like the infinity sign. 

Make 4 Tetrahedron in total. Try to arrange them in different ways. What do you imagine they could become together?

Build a squared pyramid. Like the pyramids in Egypt.

Transform your Pyramid into an Octaeder. And see if it spins.

Last but not least, try making a small sculpture of anything you imagine. Let others guess.