Bombs are an exploding object that cannot be naturally summoned by the shaman. Bombs blast mice away from where it explodes after a set amount of time or bounces, or contact with a mouse. They have a tendency to throw mice off the stage and are generally considered obstacles; however, experienced mice may consider them a helpful to push them to their goal sooner.
Bombs are lighter than cannonballs and will not detonate before fixed amount of bounces, so a mouse could try to push bombs away given the bomb hasn't bounced enough.
In older versions of the game, bombs would explode instantly on contact, but this was changed in a later update.