And either one of them is absolute hell in an airport X-ray machine....

<cleaning coffee from my monitor>

Okay. Taking this one step further into the surrealistic off topic area, what about the origin of the portable hole. I have seen it used in a few other places over time:

a) Bugs Bunny / Road Runner cartoons where "Liquid Hole" is used to create assorted mayhem...
b) The Beatles - Yellow Submarine and the Sea of Holes...

Any others?