Break Free from Ruminative Thoughts, Stay Away from Anxiety 

Animals have rumination, and so do humans.
The difference is, animals' rumination is for further digestion, such as in cows and sheep, who return partially digested food from their stomachs back to their mouths to chew again, mixing with more saliva, then swallowing and digesting once more.
Human rumination, however, is a unique psychological phenomenon.
Reflecting on Rumination: Consequences, Causes, Mechanisms, and Treatments
pubmed.ncbi.nl...
Worry and Rumination: Distinctly Associated with Anxious and Depressive Symptoms as Well as Coping Behaviors
pubmed.ncbi.nl...
Rumination as a Mechanism Linking Stressful Life Events to Depressive and Anxious Symptoms: Longitudinal Evidence from Early Adolescence to Adulthood
www.ncbi.nlm.n...
Rumination as a Transdiagnostic Factor for Depression and Anxiety
www.ncbi.nlm.n...