Square ones have the potential for falling through the hole. Round one's don't.
Okay, here's one I've been saving up.
After a forest fire, the fire fighters were policing the area, making sure the fire was out. As they were searching through thing, one fire fighter found a neoprene glove. A few feet away, another fire fighter found a swimming fin.
As they were discussing this, one of the fire fighters noticed some metal reflecting the sun up in a tree. A ladder was brought over, and it was discovered that there was a scuba diver high up in the tree, his flesh burned off from the fire. An autopsy showed a broken back. This was near the middle of the field, and there was no way the scuba diver could have fallen out of the water and landed on the tree.
How did he get there?