The Secret Triwizard Challenge

Anyway, you cast Diffindo and aim at the spider's belly. Your spell hits, and the spider's insides spill out, some of them on you. You retch as the spider tumbles to the ground, writhing and slowly dying. The professors are definitely gonna find that corpse, but hey, that's a problem for another time. For now, you've beaten the spider!
You cast Scourgify on yourself (to remove the icky spider guts), then cut through the spider webs around your ankle with a carefully placed Diffindo (can you imagine casting that spell in the heat of the moment? You would have severed your foot from your leg!). Time to keep calm and carry on into the maze.