Autistic Teddy Lupin's appearance varies to copy their interlocutor. They don't do this on purpose but it irritates people sometimes. Their friends learned to cope with that and actually got to enjoy it. Teddy got highly uncorfotable when several people talk to them because of autism but also because their metamorphoses went out of control and weird, and were tiring.
The whole class was very inpressed in Hagrid's class as Teddy started to grow a fabulous black beard.
McGonaggal get intrigued and sending an owl to the department of research on rare forms of magic when she saw Teddy, instead of metamophosing into her, getting some cat whiskers, cat ears and squares around the eyes. It happened the first time they saw her as she was in a human form and they did not know at all she was an animagus. Harry, Andromeda and Ginny thought it would be funnyer for them to be surprised the first time they would see Minerva transform.