Alternating between "still face" and smiling interaction with a baby (I'm only talking moments, here, not 2 minutes like the baby-torture video) is as good as playing peek-a-boo. Babies have almost zero social filter, so you can watch them go through all the mental gymnastics:
"Yay, we're having fun! We're having fun, right? What's going on? Did I do something wrong? Am I stinky? Why are you being so mean - Oh, we're having fun again! Yay!"