You strike the mirror with your striking hand, dealing it a strikingly accurate blow. Or strike. Whichever.
The mirror shatters into a thousand glistening fragments, each one reflecting a parallel universe. You feel a slight sting in your striking hand as a drop of blood rolls down one finger, finally splashing to the ground on a single shard of the mirror.
You pick up the shard, mezmerised by the world you see inside.