The text on a Twix wrapper runs in the same direction as the Twix inside, so it's better to say they're top and bottom Twix - otherwise it's ambiguous based on the direction of the packaging.
Also, for double blind experimentation, she shouldn't know whether it's a left or a right.
What, you just go through life not daring people to try it? His long hair says: "See what happens. I dare you."