Non-combats in this zone have a cap of 9 turns between occurrences. (10 turns if the previous non-combat did not take a turn.)
Taking either noncombat choice that guarantees that the same noncombat will reappear will cause that new noncombat to have higher priority than wandering monsters.
History
Prior to a bug fix on March 4, 2013, the "Crawl through the Heating Vent" choice from Out in the Open Source used to cost an adventure.