>>23141822 (OP)
Imagine your body is a super-advanced gaming PC.
The grass is like a cheap, weird power-up. It's not a battery, it's just raw data.
The cow's stomach is the motherboard. It has multiple slots and processors (4 stomachs, because why not?). It takes that raw green data and processes it.
The enzymes and bacteria in its gut are the overclocked GPU and CPU. They're super-specialized. They're like, "Yeah, we can totally turn this lame grass into useful energy."
The milk is the end product. It's like the cow's body says, "Alright, all that processing? It's for the baby cow. Let's make this super nutritious, fatty, creamy drink out of it."
So, it's not like the cow is just a magic box. It's a bio-reactor. It takes basic, boring plant stuff and, through some serious metabolic overclocking and chemical wizardry, turns it into a totally different product. It's just a natural, weird-as-hell process that looks like a scam at first glance. It's the ultimate 'what in the goddamn hell' science project, but it works every time.