Why would lungs of an animal that was eaten by owl not show up in pellet?

The lungs of an animal that was eaten by an owl would not show up in the pellet because they are absorbed by the owl's digestive system. Owls have a very efficient digestive system that is able to break down and absorb most of the nutrients from the animals they eat. The only parts of the animal that are not absorbed are the bones, fur, and feathers, which are regurgitated in the form of pellets.