Half and half is simply half whole milk and half cream. In the UK, they call it half cream. According The Kitchn, half and half typically has a 10 to 12 percent fat content, which, it stands to reason, means it's less fatty than cream and fattier than milk.
Dogs can eat peas safely. Peas are a good source of potassium, zinc, iron and several vitamins. Depending on the size of the dog, 1 or 2 tablespoons of peas is recommended. The dietary fiber in peas also helps overweight dogs feel full thereby reducing the dog's intake.
Re: Cats and peas. Cats are obligate carnivores, they don't need peas for moisture or for protein, they need meat. The dry foods that use peas, use them to provide the 'glue' to keep the dry food formed into kibbles....other foods use grains or potatoes. That said, if she likes peas you can certainly use a few of them as a treat here and there, but don't use them as a meat or water substitute.