Skull Goo is a species of Goo in the video game World of Goo. They are first introduced in the level Misty's Long Bony Road and only appear one other time in The Third Wheel. Here, the Sign Painter notes that it isn't clear if they are alive or dead. Skull Goos are impervious to spikes, possibly because they may or may not be alive, so they can be used to help more vulnerable types of Goo Balls (such as Black Goo and Green Goo) traverse spiked areas. Like Green Goo, they can be detached from structures and they can also enter pipes. However, loose Goo cannot traverse the Skull Goo's legs.