How can I not laugh?

Tonight I put Violet in bed and as usual I heard her talking herself to sleep for awhile. After about 30 minutes she started yelling so I went in to see what was wrong. When I looked in her crib, she looked up, smiled, then stuck her tongue out at me and started blowing bubbles and spitting. I know I shouldn't encourage her to stay up past her bedtime but I couldn't help but laugh when she pulled that one on me. The worst part was that when she heard me laugh, she started laughing too. Now I have a very awake baby who knows how to get my attention and get away with it. Great.