For whatever reason, you see the spider as the lesser threat. You stand your ground, ready to fight, when a hand shoots out from nowhere, and grabs the spider. It reacts by biting into the tender flesh, you hear a surprised scream of pain as the hand retracts. The spider gives chase to the offending hand and you see this as your opportunity to run.
You run for the crack you saw earlier, it is closest, and possibly your best chance to escape. You're thankful as you don't hear footsteps giving chase behind you, human or otherwise, and make it through the large crack in the wall.
