You get this for beating level 8. Here's a step-by-step guide!
1) Click the obvious coin in the first screen.
2) Click the caveman in the scene to talk to him. He has 3 choices that can all be selected twice.
3) Pick up all of the items he gives you.
4) Use the hunk of meat on the pig to make a bone.
5) Use the resulting bone with the black sharp rock to make an axe.
6) Use the axe with the pig to make another hunk of meat.
7) Use the axe on the other stone to make a wheel.
8) Use the hunk of meat on the bird to make another bone.
9) Use the wheel on the bone to make a key.
10) Pick the key up and use it to open the cave door. Go to the right to enter the cave.
11) You'll see a red fly get eaten by a jellyfish when you walk in. Click the jelly fish to gain control of a light.
12) With your mouse light up, go to the top left through a small tunnel to get the second coin.
13) Go to the tunnel under the coin tunnel now, and at the end of one of the forks is another red fly.
14) By keeping your light close to the fly it will follow you. Lead it out of the tunnel and down to the lower right where it will be eaten by another jellyfish.
15) You can now move to the right. In the top corner is another jellyfish you can click to gain control of a light.
16) Move to the left, and avoid the purple bugs. Go into the second indent to find a red fly.
17) Lead the red fly back up to the jellyfish you clicked on to get the last coin of the level.
18) Take the light back down to the main area and you'll find another red fly. Lead it to one of the jellyfish on the bottom.
19) Click the third jellyfish to transfer your light to it. Move to the right.
20) There are 5 columns of glyphs in the background of this room. You need to click the only glyph in the second column from the left, the second glyph from the top in the third column, the top glyph in the fourth column, and the middle glyph in the right-most column.
21) And octopus alien will pop up if you have the correct glyphs. The goal is to move him to the other purple spot in front of the woman on the right. The tentacles are directional buttons. However you cannot go in the same direction 2 moves in a row.
22) R, U, R, L, U, L, R, U, R, U, D, R, D, R, D. The octopus will grab the girl and flip his tentacles. They now point in the direction they go, instead of corresponding to a directional pad.
23) L, U, R, L, U, L, U, D, L, D, L, R, D, R, L, D, L. The octopus will drop the girl off. Pick her up and go left to unlock an achievement.
24) Set the girl down on the tile to the left, and then go stand on the tile on the right. Pick her up again and go left twice to beat the level.