Later levels have a variety of blockers that cover up numbers. These take the shape of hay bales, ice blocks, boards, bricks, stumps, and other objects.
A blocker can be destroyed by using a Blocker Breaker Power Up, daubing the number the blocker sits on, or by using a Joker or Super Joker to select the blocked space.
A Rocket will be stopped by a blocker, but will destroy it.