I used to have a kitteh who did this whenever she saw a bird close up through the window, or if one was stupid enough to get close to her outside. Sashay was a horrible hunter because the bird would have to be old or infirm not to hear that coming. Sadly, we moved and instead of letting me take the kitties over to the new house to get acclimated, my mom's boyfriend took them over and just let them out of the car in front of the house. They ran into the woods and we never saw them again. I found out about it when I got home from school and I cannot describe that feeling, but anyone who has lost a pet unexpectedly knows of what I speak. I still hope they took up at someone else's house and lived to a grand old age instead of the alternative.
Oh well, on to more amusing things:
Wasn't she pretty? She was SO mean too!....to everyone except me, that is :) I still miss her.