Sterling was terrible at getting hit by the worst possible spells at the worst possible times. Like when he had gotten the Tickling Jinx from Ben right when he had him... or when he got hit by Sectumsempra just as he was about to get close enough to distract the Slytherin girl he still didn't know the identity to... getting hit by the Cruciatus Curse right as he was trying to get Allana to listen to him...
He got hit in the chest by the spell. "Oh!" he screamed in immediate surprise just before the pain started. He fell backward and bashed the back of his head against the wall behind him.
It wasn't quite like anything he had felt before. Every nerve in his body started jumping, electrifying... it was a bit like the sensation he had when he kissed a girl... but there was nothing pleasant about his nerves standing on end. It was... literally torture. His nerves were alert like this for a split second before the pain started.
His nerves tried to jump out of his skin. "Ooh! Agh!" he screamed, the only recognizable screams syllables of screaming that escaped his throat before he started releasing the pain in incessant wails, stopping only to breath, but then screaming out again. He felt like he had been thrown in a fire... no, magma. It was excruciating.
He felt as if a billion needles were stabbing into him from all angles... swords, daggers, flamethrowers... he squirmed on the floor.
He didn't stop writhing. His overexcited nerves pushed him in every way, contorting him in positions that normally would have been too painful for inflexible muscles to handle... but that pain was by far outmatched by the pain of the curse. He felt tears streaming out of his eyes as he screamed. He couldn't think of anything through the pain, but somehow he managed to form the automatic word "Stop!" before he plunged back into his pain.