JP_Finn describes how it works in reality. The UrW logic is somewhat different, as pawboards can catch animals that just step on that tile. In your case you left the diagonals open, and I would expect animals to frequently walk around the traps to get to the center, assuming they want to go to the center.
I get animals in empty snares, small deadfalls, and pawboards because I use them to keep animals out of my farm plot area, not actually to trap animals. It's not a lot, but it happens.
When I actually try to catch animals, I make trap lines of something like 5 traps, ideally with trees along the line to make it longer. In that case I also bait each trap with bait I believe the intended prey is interested in. As has been noted in another thread, that kind of trap line doesn't work in real life, because the traps aren't directly beside each other, so it depends on how much you want to game the game in the game (couldn't resist the pun).