Mice can free himself

The spring is too weak. Several times, the bait was gone, closed the case,
but no more gefangeness animal in a trap. Through the mesh can not be hatched,
remains only too weak closing spring as a reason.
Very annoying.

Update 23:10:14:
I heard slam the trap and am back quickly.
The mouse was caught, and wandered in the case.
The next moment she was outside the case.
The flap was not moved. Obviously, the stitches are
but big enough for a mouse (6 cm without tail).