You enter the laboratory and see an experiment. How will you know which class is it?

If it’s green and wiggles, it’s biology.

If it stinks, it’s chemistry.

If it doesn’t work, it’s physics.

Two biologists are in the field following the tracks of a radio-collared grizzly bear. All of a sudden, the bear crashes out of the brush and heads right for them. They scramble up the nearest tree, but the bear starts climbing up the tree after them. The first biologist starts taking off his heavy leather hiking boots and pulls a pair of sleek running shoes from his back-pack.