Step 6: Removing the negative
Using a sharp knife, cut around the sides between the housing and the silicone.
If possible break away the sides of the housing (it will make removing the bottom much easier).
Pry the bottom of the housing off of the silicone. Because of the undercuts on the blocks, the tetris pieces will probably remain trapped in the silicone.
To remove the blocks from the silicone:
Using an exacto knife cut away the silicone trapping the blocks in the negative. Once enough silicone is removed flex the mold a bit, and you should be able to peel out the wooden tetris pieces.