Kirsten, Boomer has done this since he was really young. Whenever it was time for his milk substitute, he'd do it (When he was an older kitten and got the baby milk as a treat) ...and he still does it if I say "baby food". He runs to the kitchen and waits for his treat with his tail quivering.

He's never sprayed, and it seems to me it's a sign of total excitement, "Ohhh, I can't wait",