http://theonion.github.io/fartscroll.js/

Code:
// Fart every 400 pixels scrolled in the document
$(document).fartscroll();
// Fart every 800 pixels scrolled in the document
$(document).fartscroll(800);
// Fart every 100 pixels scrolled in the body (probably a bit much)
$("body").fartscroll(100);
// Now I'm just adding more examples to make the page longer
$("body").fartscroll(50);
// SO MANY FARTS
$("body").fartscroll(5);
// I should register fart.io for this
$("div").fartscroll(500);
// I should register fart.io for this
$("body").fartscroll(400);
// Dammit, fart.io is taken
$(window).fartscroll(600);
// Alright, that's probably enough examples
$("body").fartscroll(400);