If you were home alone in the middle of the night, wathcing a horror movie, and you heard a fart from beside you...

Jump out of my seat, terrified, then as fast as I can, grab the nearest weapon against my attacker...frebreeze, air freshener. Haha, I'm not actually physically able enough to fight someone.

A little bit of both

I'd sit there, because it would obviously be mine

Scream ...

Scream, that means someone is there o_0 then I would probably cover my nose

I would laugh then scream

I would get some salt, make a large circle and then get inside the circle. Also, I'd grab something iron.
This is probably because I have watched too much Supernatural lately.

Neither.
I would stare at the spot where the noise came from.

This question made my day

Omg for some reason I cracked up when I read this question XD

An odd mixture of both

Scream... And maybe laugh.