(In the Ice world)
After you melt the ice in the cave by playing the drums, you will head right and enter another cave with a big dude and a fish bowl.
There is a radio on the left half of the room that you can interact with. You need to set both antenna's the most jagged (zigzaggy) option. Then, the radio will eat the big dude's head unlocking the achievement.
If you can't interact with it, I had put a fish in the fishbowl beforehand (which made the dude drop a key item for me). This fish was gotten by using the teleporter thing to set it to the water/fish setting. Which fills up the box with water. That setting's only purpose is to give you this fish.