Bugs:Leisure Suit Larry Goes Looking for Love (in Several Wrong Places)
This page details bugs of Leisure Suit Larry Goes Looking for Love (in Several Wrong Places).
In one of the most infamous game-stopping glitches in adventure games, part of the endgame puzzle requires Larry to put an airsick bag in a bottle and light it with a match, but addressing the airsick bag as simply "bag" (with no definite article) results in Larry losing the bottle as if the wrong command had been given. This is because to fix a different parser bug that frustrated the designer Al Lowe, the word "bag" was redefined as a verb even though it is never used that way in the game. The result is that the parser interprets e.g. "put bag in bottle" as incorrect input, because it believes "put bag" is two verbs in a row and thus ignores the rest of the command.
The glitch was not caught until after shipping because Sierra's policy at the time for playtesting was to always use complete sentences, i.e. "put the bag in the bottle". Despite the change of "bag" from a noun to a verb, that command works because the word "the" tells the parser that the command refers to a noun. Thus, the airsick bag is the only item in the game for which the definite article is required if using its short name. Any variant of "put the bag in the bottle" and "light the bag with the match" possible in the game without specifying "airsick bag" or "brown bag" will work as long as the command states "the bag" as the subject and not just "bag".