Eric raised an eyebrow, "how can I forget, Lestrange, when I am constantly reminded?"
Not quite learning when to shut his mouth, Eric preferred to live as though he was fearless—which was far from the truth. If he had to fight using a wand, he knew he would do miserably and end up on the cold ground in the middle of an abandoned farm somewhere. Taking turns in school was a rule that did not apply while the duel was legitimate, not to mention while fighting Death Eaters.
Even so, Eric did not think Rodolphus torturing him would have been useful for the wizard's reputation. If someone thought him useful to their purposes, pissing Eric off would not serve them well in the future. Despite Eric's many weaknesses, he did not foresee himself giving into their demands while in pain or somehow disabled, not willingly anyway.
Eric could tell a lot about someone just by how they treated him and responded to his sarcasm. The more Rodolphus attempted to threaten him, the less he felt inclined to think he would, under any circumstance or persuasion, help out their purposes.