Can peas (shelled) be eaten raw? My mum thinks that there is something dangerous in them that is destroyed by heating, so they must be cooked. What could this be?
If you're talking about garden peas from a pod, my mum used to eat bags of them and they never did her any harm. I think it's just dried beans/peas you need to cook thoroughly before eating, especially dried kidney beans, there are some toxins that cooking destroys.
Your mum is mistaken. None of the peas you or your mum will come across contain toxins. There's no harm whatsoever in eating them raw. Perhaps she's thinking of raw kidney beans? These are poisonous until cooked thoroughly in boiling water.
(Tip. Don't put raw kidney beans in slow cookers. They may not reach a high enough temperature to destroy the poisons! Use canned ones instead.)