ruminating

a deer on our back lawn chewing its cud (ruminating) in the rain
The deer is one of a pair that visit us almost daily and sometimes twice a day, morning and evening. The deer in the photograph has antlers.

Humans also ruminate. 
Three forms of rumination have been proposed
1. State rumination, which involves dwelling on the consequences and feelings associated with the failure. State rumination is more common in people who are pessimistic, neurotic, and who have negative attributional styles.
2. Action rumination, which consists of task-oriented thought processes focused on goal-achievement and correction of mistakes.
3. Task-irrelevant rumination, which utilizes events or people unassociated with the blocked goal to distract a person from the failure.
(Wikipedia)