Star Wars Episode 5: The Empire Strikes Back - That Lightsaber Had Premature Contraction
At the scene when luke is in the Wampa cave, and he cuts off the Wampas arm, look and listen at his lightsaber. It makes the sound that lightsabers make when they contract, but his lightsaber is still out.
When Luke is in the Wampa's cave and he cuts off its arm look closely at where the arm came from.... you can see the joint that the arm was projected from....