"Don't tempt me," he growls, eying Severus' arm as if checking for the best place to break. "Goyle liked to arm wrestle," he says, grinning more genuinely now. "Well, he used to. And I never had any problems with him," he adds virtuously. "Severus, I sincerely hope you abused your position of authority to get back at the Gryffindors." It's more a statement than a question. It's what he would have done.
"Violent potions," he suggests hopefully. "Not archeology!" Rodolphus makes a face. "Mucking about in the dirt; now that's for children." Rodolphus gives Severus a look. "I did ask you not to tempt me. They weren't covered by my promise."