Knock-Knock doors are special, joke-telling doors located in every street of Toontown. They all seem to be closed off, and standing in front of one will trigger the door, or the Toon behind the door, to tell the person who's standing in front of them. If one decides to walk too far away from the door while the joke is being told, the joke stops being told. When the building a door is connected to is taken over by the Cogs, the door turns into a gray tunnel only the Cogs can enter and leave. This tunnel is capable of spawning more Cogs near the building. A door also counts as a NPC, as you can see an arrow on the side of your screen pointing at it's direction when you're nearby, and the door is telling a joke.
Pre-Alpha Knock Knock Joke contest
Before Alpha began, fans could have a chance at winning an alpha key by submitting a knock knock joke of their own to the Toontown Rewritten team. Several entries won, and have since then been told by the Knock Knock doors on Silly Street, Toontown Central.
List of Knock Knock jokes
This is a full list of all Knock Knock jokes in Toontown.