“ 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.”
“ 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.”
“ A small group of men stares intensely at something. Coming nearer, you see puppies, obviously still young, as they are small and only learn to walk. Cute as they are, the men look serious and exchange a comment here and there, making their mother nervous. But one man keeps her somewhat calm, while looking with others on the little ones.
The puppies are a completely new dog breed. The breeder hopes for better characteristics, the other men are mostly hunters and other dog-fanciers, that were called or came from own interest. If all looks well, they will have business. But now, they are just watching.”