Statues
". . . and this stairway leads to the Physician's chambers," their guide told the new knights.
Gwaine's gaze wandered to a nearby staircase. "Why's there only one dog statue?" he asked.
Elyan jabbed him with an elbow. "Gwaine," he hissed, "focus."
The courtier nodded acknowledgement to Gwaine. "Your friend is correct. You can see where there used to be a pair of statues, but the other went missing a few years back. No one knows what happened to it." He paused, then smiled. "If you ask Merlin, he gets a very strange look on his face. But he's never told."
I don't think Merlin ever unenchanted that dog in 1x02 . . .