"Flapping"

Derek is a "flapper."  When he gets excited about something, he jumps up and down and flaps his hands.  Sometimes he runs back and forth or around in circles too.  I like to think it's because he just can't contain his excitement.  Maybe someday I will find out.  Anyway, he usually does this when he sees something with wheels--such as a lawnmower, or a cement mixer, or a garbage truck. 

Here is a video I took of him watching his father mow the lawn.  Every time the mower went by, Derek was thrilled.