There are 7 "worlds" in the game, each with 2 or 3 levels. Once you complete World 4's three levels and see the memory of the two kids playing video games and eating popcorn you "Can" get this Achievement.
I say "can" because you have to find it in the memory. While the memory plays you can move left or right to play the memory or rewind it. Keep playing through it until an object in the area shakes and makes a sound, once that happens freeze on that scene and a little box will appear and unlock the Achievement.
In order to get this one, you have to rewind until the poster on the wall starts to shake, then freeze the screen until the little box appears from behind the poster. Below is a video for reference.