Imagine holding what appears to be an average worm when all of the sudden it spews a web-like mass all over your hand and then begins to undulate its body in a creepy fashion.
That's exactly what this video of a ribbon worm shows:
According to Encyclopedia Britannica, the worm from the phylum Nemertea is typically found in marine environments, but a few are found in freshwater or on land. The white, ribbon-like thing that came out of the worm is a muscular proboscis that's typically used to nab prey. In some cases, it can help the worm burrow.
Here's a video of such a worm swallowing its prey whole:
If you thought these videos were fascinatingly gross, check out this one from last year of a leech swallowing an earthworm. Gulp.