What makes people laugh?

What do people find funny, or what is it that makes them laugh? 

Below are things that make some people laugh:

"Humor to me is anything that makes you laugh.  I think of SAC and sarcasm; I really enjoy sarcasm."

"Sarcasm. Irony."

"I guess things that are a little ridiculous or out of the ordinary.  But normally only if everyone involved in the situation is alright."

"I usually laugh at funny faces."

"SAT prep, friends getting hurt, Wilfred, puns, people that try way too hard (for example, getting dressed up for school)."

What is Literature and What is Civilization?

Seemingly simple questions that aren't so simple.