I was rather amused by this fannishness promulgated by </a></b></a>foreverdirt, and so, despite not really doing the OTP thing, I thought I'd have a play around:
In janecarnall's words: One half of a couple is standing in the fresh vegetable aisle of a large supermarket. The other half is away over the other side of the shop. The two can see each other, but cannot communicate verbally. Can the other half convey to the one in the vegetable aisle that he wants broccoli?
Marcus conveys his desires in crisp, clear-cut, if flamboyant gestures. Susan briefly considers being deliberately awkward, but picks up the broccoli eventually.
Susan on the other hand has to restrain her impulses to shout pointlessly across TESCO while Marcus shows her various outlandish vegetables. In the end he selects something strange and fractal which he insists is true British broccoli.
Ce'Nedra shouts across the supermarket like a fishwife, causing everyone to turn and look at her. Garion, OTOH, has never seen outlandish foreign vegetables like broccoli so buys a rutabaga.
If he actually knew what one was, Garion would have no difficulty using the Will and the Word to instruct Ce'Nedra, but she'd probably be in a strop with him and misunderstand intentionally.
Whatever it was Susan did it caused Draco to double-up with laughter, but there's nothing else that she could possibly have intended, so he gets a bag of mushrooms.
On the other side of the test, Draco entirely fails to think up any way of gesturing that passes the snigger test, so makes up an on-the-spot modification of the Morsmordre charm. Unsurprisingly this causes havoc.