The second Chrome Dimension level can be unlocked from a chrome ‘egg’ found in Level 1-18. You will need to zoom out to see the egg. The Chrome Control guide will have more information on zooming out on different computers.
The first white bird should be used to hit the middle portion and make that part collapse. The second black bird should take out the right side of the brain, and the third bird should be used to take out the left side of the brain. It may take a few tries to pop all the birds.