Hissing, Sludge was tempted to use his acid blood, then decided to try something else. Sticking the end of his sharp tail into the lock, he wriggled it around and found, to his surprise, the door came open with a small click.
He stepped outside, staring up at the trick-or-treater in the tree, and blinked as he was tossed a rolled up piece of parchment which hit him in the head.
Well, apparently he was a knob now, whatever that was.