We were crossing a ridge when Corgan was lifted off the ground by something. "Shoot it! Shoot the tyrannosaur!" he screamed as blood streamed from the puncture wounds that had opened up in belly. I fired into the empty space above him to no effect. Then Corgan's ragged corpse dropped to the forest floor, and I was alone. Utterly alone. There was no dinosaur. There was nothing.
The PCs see a large oak tree, a curious species of yellow and black butterflies swarm around it. Upon further inspection they find that the tree is hollow and that there is an underground cave in it from which the butterflies appear. Will they inspect this strange cave?