Wooden Dowel: The Hydraulic Relief ValveWhy flat-pack furniture pins aren't perfectly smooth.

From the show

Why it looks like that

Assemble a bookshelf and you will encounter dozens of these small, grooved wooden pegs. While they look like cheap connectors, their textured surface solves a complex fluid dynamics problem. This episode explores how these spiral or straight cuts prevent hydraulic lock, allowing trapped air and excess glue to escape without splitting the wood.