Escaping mice

Remember those world war II movies where the prisoners tunnel there way to Freedom?

This story is almost like that.

One day i look through the door window in an animal room and see a mouse walking on the floor.

OOPS where does that one come from. So i go in the room catch the mouse and leave the room. Then the next morning again i look through the little round window in the door and see again a mouse on the floor.
Of course i also go out and catch this one. Ok strange but true all the cages where closed properly and i didn't find any other loose once.

But then when i start changing the cages i find an empty cage..... and the card says that there should be two mice in that cage.

And then i see what happened. This cage has a big hole in the bottom corner, big enough for a mouse to get out. I never found out how the hole got there (the cage is from hard plastic) but i found there escape route.