An extremely versatile question. Can be used to kick off furious debate amongst pretentious philosophy students (pretty much a tautology, i know), who think it is a genuine poser worth considering rather than a clever way of exposing how pretentious they are. Also makes for great drunken pub debate when everyone's pissed enough to get angry with each other for their opposing views.
Yet the shark/lion dilemma represents so much more than this. I for one, would recommend it as an icebreaker in any conversation, and encourage you all to try it out. When considered, paradoxically, as a genuine question, the possibilities for exciting debate are enormous, as are the vagaries of the fight itself. Generally speaking, the question of whether the shark can move in traditional swimming patterns, the weaponry employed by each, and whether the atmosphere of the moon is conducive to their breathing, are moot. Although me mate Dave swears blind that it's obviously the lion.