If one suffers physical trauma and/or becomes somewhat dehydrated, he may suffer a low-grade fever.
Poor Theodore! His run-in with the side of a desk the other day resulted in quite a bit of swelling. He was quiet most of the day yesterday and did not eat one bite of food (not even ice cream) or drink much more than a couple of sips here and there. All this craziness put his body on guard with a temperature of 100° today.
After eating and drinking better during the day today, his energy is on the rise and his temperature seems to have returned to normal.