Each year, the first night at Hogwarts was a mess. While the 1st year were lost and often tried, voluntarily or not, going to the girls room and getting ejected, the older students were celebrating getting back together, speaking about what they've done in the summer and complaining about their teachers. Harry, after getting a lot of attention for shaking Snape hands without dying, was a little bit too excited and tired. For the first time of his life, people knew him and were nice without trying to trick him into a fight, unlike Dudley's friends. Suddenly, two tall and rather agitated ginger came up :

"Hey Harry, it's a huge honor to meet you. You're the first first year we've ever met..."

"...to avoid death twice already..."

"...The first time with the Snape-Man-We-Should-Not-Talk-About, and the second time..."

"...while saluting your new potion teacher, Snape."

"As your biggest fans, we offer you, for free, a way to survive your first hour of class with him"

The two were completing each other sentences so fast Harry was confused and answered :

"I'm going to have classes with Voldemort ?"

The twins were so confused about the fact that Harry just said 'Voldemort' out loud, while simultaneously thinking Voldemort could be a teacher at Hogwarts that Fred choked on a weird looking peanuts he was eating, and had to be driven to the infirmary. While his twin was surviving an unexpected death, George concluded that Harry was either a comedy genius or completely insane. In both cases, he was exactly what they were looking for, and their plan would be working perfectly.