There was something in the Merlin's smile that puzzled Arthur.

The servant was always smiling. No matter how disgusting were the tasks that the prince commanded. He, at first, always twisting the nose, but always fulfilled.
Merlin could complain, but when Arthur's clothes were properly washed and ironed, polished their armor, your room tidy and your food on the table waiting for you, all at a time that would have to be 5 Merlins to happen.
The prince had been waiting since hidden behind a curtain of the castle, out of his room, just to see if the servant was receiving help from someone. But nobody helped him. He did everything himself, with a smile on his face and sweat marks the end of the day.

And he has more respect Merlin for that.
(What he did not know was that magic could be more efficient than 10 Merlins.)