Making all the crazy non-Euclidean conversions between seeing and seizing, you fling out your free hand and hey look, you've actually got the darned thing. You haul the object up without sending either yourself or the magic mirror overboard, straining only plausibility. But this is a dream.

The scourge of the surreal seas squints down at your prize. "No, not that one," she complains. "I meant the purple thingy behind it. Oh well, it's gone now."