“ Orcs record their deeds through symbolic mutilation, scarring and tattoo. Perhaps creating the medium of skin as art, which humans followed later. Perhaps tattoos remind the elves of orcs and make them angry...”
“ After building a new granary,it is customary to let a rat feast on grain. After that,there is chase and the rat is killed. Failing to catch this rat is a bad omen.”
“ 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.”