With the following code (and jquery.js include file):

$(document).ready(function() {
  $('.element').click(function() {});
});

Object.prototype.dontcallthis = function() { alert(2); }
Object.prototype.obscurefunction = function() { alert(3); }

Clicking a .element causes both extension functions to be called, resulting in a 2 and a 3 popping up in alert boxes.