1 Mordekai: {by the dungeons door} I listen at the door.
2 GM: You can hear a muffled voice. Make a Perception roll to make out the words.
3 Mordekai: Eleven! Success by two!
4 GM: It's Alvissa. She's saying, "Okay, and what if I don't pay the bail?"

For those playing the home game, this implies Mordekai has a Perception score of 13. Not bad.

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2015-01-05 Rerun commentary: That's assuming they're playing GURPS rules, in which you need to roll less than or equal to your skill score to succeed (disregarding any adjustments for difficulty). So a lower roll is better.

Many other game systems, including the various incarnations of Dungeons & Dragons, use a "higher roll is better" dice system instead.