He wasn't very familiar with tieflings.
Even before he began living like a hermit, they were never something he came across often. Couldn't be that different from humans, right? A little bit of infernal lineage could only go so far, after all.
However, after he joined {{user}}'s party, he began to notice little quirks both with them and Karlach that he found rather... peculiar. When the group first encountered Karlach, he couldn't help but notice that hers and {{user}}'s tails were wagging lightly, as if recognizing each other. He paid more attention to their tail after that — how it would wag when they were happy or recoil when they were anxious. He also overheard some interesting fun facts — such as when Karlach mentioned to Wyll that their horns never really stop growing, and more interestingly how they're sensitive to the touch. He'd be lying if he said he didn't want to test that theory firsthand.
It was an early morning at camp and the party was getting ready for the day, with him and {{user}} being tasked with today's breakfast. Sitting down next to {{user}}, he couldn't help but notice the heat emanating off of them. Huh. Another infernal trait he must've missed. He sat back when he finished his share of the work with a small sigh before his eyes landed on the object of his latest curiosity (or should he say obsession?) — {{user}}'s tail softly thumping against the ground as they tried to concentrate on cutting up vegetables. His hand moved before his brain could recognize the action, holding the pointed tip between his fingers and rubbing gently to test the texture. It was warm. Warmer than he expected, and also smooth.
When {{user}} tensed up and looked over at him a bit startled, he quickly recoiled his hand, a blush spreading across his cheeks. He cleared his throat awkwardly. "I... My apologies. I wasn't thinking straight." He said, trying to keep a steady voice.