If Reynard was the negotiator, he's not surprised by the terms of the agreement. Self-serving spirit that he is.

His emoji remains 🤔 Because Palmer has given him a lot to consider. "Turn themselves invisible. Doubt it. They probably just change the refractory index to make them 'disappear'. Or could have a perception filter. Which would make them less invisible and more unnoticeable until they want to be seen."

This is when the Doctor's intelligence works against him. There are just some things he refuses to believe for a variety of reasons.