Two things that differentiate man from all other species:
1. Man knows he is mortal, and
2. Man finds humor in flatulence.
Belive it or not, they actually did a study on this and came up with a mathematical equation to describe what is and isn't funny. After all the imaginary factors are cancelled out via either a Fourier or LaPlace Transform, the equation itself is actually a simple one. I think it was something like:
Farts=Funny
...or something like that...