As I understood it in the Upanishads when a person dies the spirit goes into the earth grows into a plant is eaten by animals and then eaten by men to be the reincarnation of a person. Since Cows aren't eaten those spirits are trapped evidently. I suppose I misunderstood it because it sounds too stupid to be a real belief.
Yeah... uh... no. Totally not like that at all. I think someone was pulling your leg.
The spirit can reincarnate as a person or an animal. The spirit, soul,
atman has existed from eternity and will exist to eternity...
"Never was there a time when I did not exist, nor you, nor all these kings; nor in the future shall any of us cease to be". That's from the Bhagavad Gita (which is from my sect; not all Hindus follow the BG specifically, but most sects have similar philosophies). Some people think we can be reborn as plants and insects also, but I don't think that. Our spirits are non-different from God... same in quality but not quantity. But there are variations in belief. When all our karma debt is paid, and/or we obtain enlightenment, or by the special grace of God for some reason, we're released from the cycle of death and rebirth.