Three programmers walk through a park and pass a bunch of trees.
The first programmer says, "I do not think there is a tree in this park."
The second programmer says, "I disagree, I think there is a tree in this park, and it's an apple tree."
The third programmer says, "No, I think the first programmer was right, I can't see a tree, and even if one existed, you wouldn't be able to identify the type of tree without closer inspection."
They keep walking through the park and come upon a squirrel running across the ground. The first programmer kills the squirrel with his shoe.