When the first human laughed after being introduced to him, he carefully examined his appearance in a mirror the instant the meeting was over. He was rather average for a Vulcan, his hair wasn't sticking up, he was properly attired and his clothes were properly fastened. There was nothing stuck between his teeth or on the bottom of his boots. There were no noticeable spots smudges or stains on his attire or his person. He could see nothing about himself that would cause such a reaction as the one the human had.
It was after several introductions that he saw the pattern. The humans would either laugh, begin to laugh and catch themselves, or look as if they were suppressing laughter while simultaniously attempting to express pity for him after his name was given.
What was so humorous about the name Susan?