From the Latin, ruminaire, to chew over again.
Foregut fermentation leads to rumination.
A good thing in cows, who regurgitate their food,
chew it over, get all the nutrients out.  

Rumination in the human mind
comes from forebrain fermentation.
Thoughts fermented fester and rot.
Humans regurgitate their thoughts,
chew them over to get all the suffering out.