In a quiet moment, we burp up old thoughts in order to chew them over a little better
Long story short, cows like to lie down to ruminate. And so do I.
Grazing animals have a tough job: they have to break down the cellulose in plant matter in order to extract nutrition from it. Grass is tough stuff, which is why cows have four stomachs. This practice also lets the cow bolt down its food now, and wait until later to chew it. That's a handy ability, when you're a shy grazing animal on the run from predators.
Rumination is a quiet, calm practice. Animals only burp up and chew their cuds when they are relaxed and at peace. On a lovely sunny afternoon you may see an entire herd of cows lying down in a field, staring off into space and chewing mindlessly.
When humans ruminate, it tends to be a more morose affair. We tend to store past slights and misfortunes, only to burp them up later at a quiet moment to chew them over. The metaphor is as robust as it is apt. In order to digest these slings and arrows, we have to process them first. We have to chew them down into paste, wringing every little bit of knowledge and perspective out of them.
A cow ruminates silently on its own. Cows don't share their rumens. You can't just give it to someone else to chew; you have to chew it yourself. That blob of half-digested thoughts is yours alone to process. Although it's nice to have someone else to bounce thoughts and ideas off, in the end it comes down to this: you, alone, with your thoughts.
I often ruminate while on a long drive. Being alone in the car gets me thinking over things, turning them over in my mind. Typically things I can do nothing about. Frankly, it often seems like a waste of time, which is why I always try to remember to bring some podcasts along to distract me.
We can also ruminate in the positive sense, of course. Before starting a new business or making a life-changing decision, it's wise to spend some time pondering it first. Rumination gives you a chance to think over all the angles and consider ways in which you can make things better. It's a good way to plan, if you have the time!