Dean made a vague sort of apologetic sound that was probably not all that convincing. He didn't know about the tail specifically, or he might have avoided that area. Possibly.
Dean could feel the tension, after a few moments, and started figuring out how to rub at the little knotted muscles under his fingers.
Dean rolled his own shoulder, feeling the awkward stretch from leaning and grunted, turning to kneel on the bed instead so it was easier to lean over Seamus. "Tell me I'm the most brilliant mate ever," he ordered, fingers working a little lower on Seamus' shoulders, carefully.