Infants are quite fond of the “peekaboo” game. The game is simple: Show them your face, then take it away.
It’s essentially two components: “I’m here,” and “then I’m not.”
“I’m suddenly right in front of you, then mysteriously, not-so-much.”…
And while you’re not there, they enjoy the anticipation of you coming right back in two seconds. (The first four hundred times you do it gives them a sense of the pattern.)
quoted from Babyhood