For beating the second level. Here's a step by step guide:
1) Start by going back to the left screen. Here, click the stone on the left to climb into the background.
2) Go back to the middle screen while in the background. Click the loop of thread (tendons??) on the right to reveal the dragon's brain.
3) Click the brain once to open the dragon's mouth and unlock an achievement.
4) Go back to the left, click the rock to get back to the foreground, and then finally back to the middle screen.
5) Go to the right to climb into the dragon. In the top left area, hidden by the trees and the dragon's spines is the first coin.
6) Now click the red blob that is second from the right to pop open the dragon's toenail in the lower right. Here's the second coin!
7) Click the leftmost blob. Pick up the rock on the ground, and head back to the middle screen.
8) Here, a different toenail has flipped up. Click the exposed part to open the dragon's brain curtain again.
9) Click the brain twice so the dragon's nostrils are open. Click the right one to throw your rock in.
10) Click the brain twice more to flip the tail up. Head to the left.
11) Now that the tail is up, the last coin is exposed, along with a rock you can pick up. Once you have the rock, return to the middle screen.
12) Open the brain curtain, click the brain to open the nostrils again, and throw the second rock into the dragon's nose.
13) Click the brain until the dragon's mouth is open again. Walk in to see the firefly get pushed out of the tube. Leave the dragon.
14) Back in the middle screen, the rightmost rock in the background will be wiggling. Click it.
15) Now click the middle, and then left rock as they start wiggling.
16) Open the dragon's brain again, and click it until his tail is up.
17) Head to the left screen to see the firefly fall out of his tail and click it to beat the level!