This is a trick I picked up when I first started selling Thinking Putty in bulk. I have seen lots and lots of people try to separate putty into two pieces by stretching and stretching. This takes forever and creates a long strand of thin putty.
Hold your Thinking Putty as seen in the photograph. Dig the nails of your thumbs and forefingers into the putty.
The tear is going to be made by only one finger. In this example we are going to tear towards us, using our left hand (because Crazy Aaron is left-handed ;-).
With a quick and sure motion, use your left forefinger to rip the putty towards you and to the left.
On the first couple of tries, you may end up just stretching the putty. Try to move quicker with more force.
Normally, when you stretch the Thinking Putty, the molecules realign themselves with the direction of motion. Herding together like sheep, they stay attached to each other and let you stretch.
By moving quickly, you don't give the molecules inside the putty time to realign themselves with the direction of motion. Instead of flowing, they tear apart.