A prehistoric human has a giant sloth, a smilodon, and a tree branch full of leaves. He needs to transport all of them across a river. His boat can only fit two creatures. Him and one other thing, which means he must take them one at a time. Here is his problem. If he takes the smilodon across, the giant sloth will eat the leaves while he's gone. If he takes the branch, the smilodon will eat the giant sloth while the man is gone. But nothing happens if you leave the smilodon and the branch together. How can he transport everything over the river without losing any of them?