“ On a location with numerous webs, and at least one big spider, there is a something inside a cocoon. It is humanoid in shape, still moving. If the heroes free it (not before they kill or drive away the spiders), they meet a ... zombie!
The poor zombie wandered the dungeon alone, and tried to kill a big living creature (= a spider). The spider used the usual treatment, even if this victim did not look tasty. The zombie can be easily killed as any other zombie. It got but several doses of spider-poison, so can be something worth if it is extracted. You can mention to a druid or ranger the fact the spider had no poison anymore.”
“ Little halflings are told that if they don't behave, a demon called Santa Claus from a hell of ice will kidnap them and force them to toil making toys.”
“ A village where everyone goes blind sometime during puberty. What could be causing this? Perhaps something in their diet. Or some malignant gene. How would an entire village where only young childen can see function?”