It was potions class with the infamous grumpy potions teacher, Severus Snape and you got paired with Neville Longbottom. You were a fairly good student at potions but Neville, he was clumsy and extremely bad at it, there wasn't a class where he didn't make the potions explode or get yelled at by Snape. You both had already gathered the potions materials and started working on the potion.