In Area B: Room 2, during the puzzle "Moonshot", a tiny connector can barely be seen on the texture of the Moon. By hitting the connector with the red laser, the Moon will begin to rotate until the dark side of the Moon comes into view. The bright symbol seen on the face of the Moon is the Aperture Science logo from the Portal series. However, another small white speck can be seen on the very top of the logo.

Afterwards, in the puzzle "Man on The Moon", after launching yourself over to the forcefield, you can find a small key hidden just to the right of it. After returning to the other side of the wall, use the far-most fan to launch yourself onto the arches to the left, and then maneuver your way to a viewfinder that is unlocked by the small key. The viewfinder allows you to get a better look at the speck on the Moon, which is revealed to be Wheatley from Portal 2 staring back at you, in reference to that game's ending where Spoiler:Wheatley is sucked into a portal on the surface of the Moon.