A cornish game hen is the same exact thing as regular chicken. They are the same breed. The only difference is the age it is slaughtered.

Most snakes will eat more then just one type of animal. Rats, mice, african soft furred rats, gerbils, hamsters. They are all prey even though they are different species. I had a ball python years ago that would eat anything. I fed him mice, rats, gerbils and dwarf hamsters. I am a little confused about your question. "so if mice and rats are 2 different animals, then why does he even show any interest in the rat?"