We just learned about a Spider's Hearts and Blood.
In a spider's abdomen they have things called silk glands that make the silk that they use for their webs.
The silk starts out like a liquid, and gets squished out through small tubes called spinnerets.
The spinnerets spit the silk out like tiny strings, and they spin all the strings together to make a strong thread.
(from: wikipedia - spinneret (spider))
Kid Facts - Blast from the past: Moray Eel