Failing to get the Ed skip

You can leave the screen one frame before Ed enters it. When that happens, you'll miss each other. You'll get past him, and he won't spot you, meaning he'll continue his way downstairs as if nothing happened. A strange side-effect is that, if the screen you entered is the corridor where the Green Tentacle is, the Green Tentacle won't move and you'll be able to get past him. Currently there's no known application for this glitch.