The Secret Triwizard Challenge

The underbelly is where the spider is most vulnerable, so you aim your wand there and cast Stupefy. Your spell is pretty powerful - the spider freezes instantly.
But the spell won't last long. You can already see the spider flexing its feet, itching to get moving again. You run as fast as you can to the exit, making it through just in time. The spider shrieks in rage and claws into the pathway, but it's too big to enter. You sigh. That was close. There's no time to waste if you cant to win this race, though.