We've discovered that Jack loves watching funny cat/dog videos on the internets. Unfortunately, this means that we have to be very careful about what we click on when we're visiting youtube. Some of those (OK, A LOT of those) videos just aren't appropriate for a 3 year old - let alone a 30 year old.
Anyway - here is some video of Jack laughing at this video.
And here is another one of our favorites. :)