The Herd
The herd is supposed to be a community and family and have a duty to look after one another. Ironically, after Thidwick doesn't reject his guests, the herd ironically leaves him behind to thrive and survive by himself in the winter. Here, Dr. Seuss may be commenting on the unkindness of society towards those who are vulnerable.
Guests
The insects and animals surviving on Thidwick's antlers are ironically referred to as guests. This is ironic because they act nothing like guests; they are incredibly rude towards Thidwick and take advantage of him.
Kindness
Although Thidwick is being kind and showing generosity towards his fellow creatures, he is essentially punished for his kindness. Usually, kindness is rewarded in children's literature, but here Dr. Seuss is showing how kindness can be taken advantage of.
Thidwick's antlers
Thidwick's antlers are his, but the insects and animals living on them ironically believe that the antlers belong to them. This causes Thidwick considerable misery, as he is too kind to tell them to leave.
