Jumping up onto the bed and settling there nicely, it wasn't long before Tim fell asleep, though he was sure to burrow under the covers first. It wasn't warm these days, even when he wore his puggish coat as he did now. When Terry climbed into the bed, he bundled himself close, and then he slept.
He was tired. That was the only reason he would ever be able to give as to why his animagus form slipped away in his sleep, particularly given that it had never happened before.
Hours later and into the night, Septimus was lying asleep in Terry’s bed with absolutely no clothes on. That was another thing. One had to be conscious and concentrating their magic to ensure that their clothes survived the changes. He'd find them all in his office later, but for now, he slept soundly, pressed close to the other keeper for warmth.