This is a bit silly, but I just spent 10 minutes trying to figure this out so in case someone else gets stuck with it, here goes:

Most jQuery events allow you to pass in an event handler with a parameter. For example, the click event has the following overload available: .click( handler(eventObject) )

Of course, I didn't read the documentation and I assumed that the eventObject was the object that the event happened to. This is incorrect - the event that the object happened to can be obtained from the implicit this local variable. The event object is actually an object that contains more information about the event itself. The full description is available at http://api.jquery.com/category/events/event-object/. In most cases you are unlikely to need the extra details... this is good enough.