1. your lips
2. i can think of a number of scenarios - but if 2 men were dying of thirst in the desert, then each given a big glass of water - the one who drinks his fast may survive, but if the others drinks his too slowly, then he will not get enough water and will just die of thirst.
.. that may not be what you had in mind, but it still works ... and i can think of a few other scenarios that would work too..
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chance favors the prepared mind.