OK, they're not that big. The white one is a lacrosse ball, BTW. The reason I have them is that during my flexibility session on Monday, Peggy had me using a lacrosse ball to roll kinks out of the back of my calves and a tennis ball to do the same thing to the back of my big, meaty thighs.
The folks at Sports Basement confirm this is a common use for lacrosse balls and pretty much the only reason they sell them, and in fact they don't sell any other lacrosse equipment.
I also picked up some Ride Your Bike To Work Day swag as I was cruising down Market Street even thought I'm technically on PTO and was only riding to the gym.