Spontaneous laughter

Elizabeth has been giggling for quite sometime now.  She giggles on the changing pad when you tickle her  belly and under her arms.  She has recently started giggling when you hold her up in the air above you head and lift her up and down and just today I started giving her a little toss and she laughs even harder!! But this afternoon she giggled for the first time spontaneously.  We were standing at the bottom of the stairs and I was holding her on my shoulder with her looking up. Pancake started running down the stairs and Elizabeth broke out into laughter!  It was the best!!! We still haven't gotten it on tape yet, but hopefully soon.