Physics Teacher: "Isaac Newton was sitting under a tree when an apple fell on his head and he discovered gravity. Isn't that wonderful?"
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.
Don't LOOK at anything in a physics lab.
Don't TASTE anything in a chemistry lab.
Don't SMELL anything in a biology lab.
Don't TOUCH anything in a medical lab.
and, most importantly:
The elephant asked the camel: "Why do you have your breasts on your back?"