Clear Plastic Cups at SEATAC

This is about airport security, not code security ;-)

Raymond has a blog today about airport security, and it reminded me of something that always puzzles me. The Seattle / Tacoma International Airport has, as you can probably imagine, several STARBUCKS® outlets. And as you may already know, STARBUCKS® has two basic kinds of cups for its beverages:

· Hot beverages are served in opaque paper cups

· Cold beverages are served in clear plastic cups

The weird thing is that they have signs up saying that the clear plastic cups cannot be taken through the security checkpoints.

Why?

It seems to me that you can hide just about anything inside one of those paper cups, but they don't get searched. I once walked through the metal detector with a paper cup in hand and was asked to step aside for a further search. I sat down, put my coffee on the floor, took my shoes off, undid my belt buckle, and stood there while they double-checked me with the wand. They never looked in the coffee cup. I just picked it up and went on my merry way...

You could also try to hide things in the clear cups, but the security people are more likely to be able to see something sitting inside of it (especially if the thing can't be submerged in a liquid) than they are a paper cup. Seems to me that both kinds of cups should be treated the same -- ban both or allow both -- but if you are going differentiate, why do it in favour of the opaque cup?

Does anyone have the answer?