Note that the bait stick is made from a hollow reed. The penny is laid out to show scale. That hole on the left is designed for the hollow reed to be staked into the ground. Another reason to have the reed hollow is that the middle can be carved out and fitted with bait (seeds in this case). This one is glued together with pine pitch glue. The idea is to get the bird to peck at the bait and that first peck is what springs the trap.