A fifth grader looked down, so her teacher asked, "What's the problem, Carol? I hope it's not homework again."

"Well, uh, yes it is." replied Carol. "I made my homework paper into a paper airplane."

"Carol, that wasn't a very bright thing to do," said the teacher, "but this once I'll let you just unfold the paper and hand it in."

"Oh, but that won't work," said Carol, looking even sadder. "You see, the plane was hijacked¹."