The Professor turned out of a side street and wandered toward him, lost in thought and idly looking in shop windows. He thought he saw, out of the corner of his eye, someone he really hadn't wanted to meet again.
"You're in a good mood," he said sarcastically, and was about to ask him if he'd taken over any planets lately, when he actually looked at the man.
"Pardon me," he said, a little flustered. "I thought you were somebody else."