Ketchup fan? Then you know you’ve got to shake that bottle of your favorite brand before you squeeze it onto your food of choice. Otherwise, you’ll be met with a watery mess followed by some gunky globs. That’s because ketchup — along with a whole host of other substances ranging from clay face masks to printing inks — is thixotropic. When it sits too long, lonely and unused on a diner table or in the dark abyss that is your refrigerator, the concoction separates and the tomato-y part thickens up, becoming more viscous. But when you shake it, everything mixes back up, thins out, and you’re good to go.