It's new. Of course it is, and Tony is fully aware that he's pushing some physical limits. He tilts his head, giving Bruce a look that's more gentle than teasing for a moment as he watches the alert tension return to his face.

"Sure. It's an idea. I can always stick to the light stuff if you want."

He's not actually going further than that as it is. The pace doesn't increase, and Tony doesn't apply any pressure. He just keeps the steady rhythm of his hands, letting the pattern sink in and imprint on his partner's nerves. Tony's already crossing a lot of lines, and he's not going to turn the whole situation upside down just to push them too far. There's a fine, calculated line between "new and exciting" and "new and horrible", and he knows where to keep it. Tony kisses Bruce's stomach again, going back to the familiar and pleasant. They don't have to cross any barriers here. He's content. Just the casual pattern of his hands and mouth marking the same areas of skin should put Bruce at a little more ease with this.