"Hey, doesn't this look exactly like the INSIDE of a skull?" "Uh, Jimmy... how would any of us know what that looks like?" "Oh, uh... never mind..." YIIIKES. Even that conversation alone would be creepy. The still-definitely-alive embryo thing as the players walk deeper into the cavity of what used to be a massive creature? Creepy doesn't even cut it. Wow!
Great / horrific concept, with lots of detail. The background is fun, but please increase the opacity of the boxes behind the text to make it a bit more legible.
As post-jam polish, consider adding a printer friendly version without the background, or with a zoomed in and B&W version of the background.