The audience in QI are sometimes invited to answer questions. On various occasions, they have received points or forfeits and been given scores at the end of the episode.
They first received a score of -45 in "Creatures", when one man received a forfeit for shouting "Dwarves" out as the answer to a question. However, Fry did not announce this at the end of the episode. Their first win was in "Death", where Fry announced their score at the end of the episode and declared them the winners. Despite this, he said Alan finished in third place, which implies that the audience weren't officially counted.
Sometimes, members of the audience are experts on the subject of a question, and Fry discusses their work with them.
See also: Category:Audience scored points.