World of Goo

In Chapter 2, "Beauty and the Electric Tentacle", pan to the left and you'll see a pink head. The goal is to make the pink head fall off the left side of the power lines. To do this you must use all the pink balloons and place them on the right hand side to make her roll off, Once successful, she'll fall and break into a million pieces and if you had followed her descent, you'll see a sign that reads, "It's so Simple" "From the Original Sign Painter". When you read the sign the achievement unlocks.