I knew I had a mouse in the basement and wanted to use a humane way to catch it.  I used the trap with just a little peanut butter as some reviewers have advised, and for a couple of weeks absolutely nothing happened (even as the fresh evidence of the mouse continued to mount all around it) to the point that I was ready to dismiss it as ineffective;  then one day I happened to glance at the trap and saw it had "sprung".  No movement from inside, but it felt a bit heavier than it should have if empty, so I steeled myself for the possibility of finding a starved-to-death mouse carcass inside...or having a live mouse jump out at me...okay, actually I had my son open the trap, well away from the house...apparently the mouse was alive and well, and is now living somewhere else.  Happy ending.