Begin with a regular sized empty foil or plastic bag of potato chips, or
other snack food and a 6-inch high stack of empty pizza boxes or textbooks
of various sizes, since you're probably not using them.
Arrange the stack from largest at the bottom to smallest at the top.
Position the bag, with opening upward and within 2 inches of the top of the
stack, and anchor the very bottom of it with a heavy object.
The mouse will smell the food, climb the stack, and fall into the bag.
The slippery sides will trap it, and the mouse's movement will produce a
loud rustling sound to alert you that the trap is occupied.
Simply take the bag, fold the top over to prevent escape, and release the
harmless little guy outside.