The PCs discover a large white ball in the branches of a tree, or in a niche in a cave. Unless magically examined, or by a PC with a specialty in insects, it is a plain, smooth white ball. After a short time, it hatches and releases hundreds of spiders, cockroaches, some other nasty bug
A corpse lays at the side of the road, or path. The man has been robbed of everything but a few tattered pieces of clothing. It looks like the scavengers have been working on him for a few days. The smell is ghastly. What dangers lay ahead?
Not every prophecy needs to be meaningful to effect a game. In the Lord Dunsany play, The Golden Doom, a child's scrawl has an entire kingdom struggling to puzzle out what sinister prophecy it portends.