Threat or promise was pretty much the same thing, at this moment.

Gen was surprised by the sudden attention to the scar - it was just a little tender - which definitely made it more sensitive. He squirmed just a bit as Senku licked there. Pushing things quite a bit - or just encouraging Senku's mood - he reached out with his unbound hands, to gently stroke Senku's ears.

"But don't you like it when my hands are free, Senku-chan?"