“ Another real world thing. White tea. Can only be picked two days a year, the two days before the flowers blossom. Could be a similiar plant that...is the deadliest poison known, cure known diseases or psychosis, or a potent herb that just tastes awesome.”
“ A small, primitive village has yet to discover fire, which is a good thing because there are highly flammable (but not otherwise dangerous) gasses in the air. The heroes, blissful in their ignorance, don't know that and think it a wonderful idea to show the locals open flame.”
“ The party comes across a nice hermit in the woods. He gives them food and lodging for the night. They awaken to his terrified screams. 'East! It's east! Stop it! It'll kill us all!' The poor horror-stricken hermit dies thrashing in agony, one boney arm outstretched, his finger pointing to the east.”