We've all seen it - a villainous creature (or person with retractable claws, especially fingertip ones) holds out a paw/hand and then suddenly extends its claws - normally without any accompanying motion - in order to imply a threat or to punctuate a verbal one. A great example is in the Adventure Time episode entitled 'Dungeon', where the Demon Cat tells Finn, and I quote: "You're trespassing in MY dungeon, manling...and I'M the thing..."
- insert claw extension in middle of dramatic pause*
Hello, Unknown Troper. You'll need to get known to lend a hand here.