Fire: Ungh's Quest

You get this in the fifth level for popping the frog thing.

Once you have the animal transformer opened:

1) Change into the mouse. Go to the left screen
2) Click the little gate at the bottom of the tree, you'll climb up and push out a cork
3) Back to the middle screen, and change back into Ungh (the caveman) and pick up the cork from in front of the animal selector.
4) Go put the cork in the frog's butt on the right screen. Back to the animal transformer.
5) Change into the bee, go to the right screen, and click the orange flower.

Pop! Both the frog and this achievement!