If I were you, I'd give up on this idea. Simply don't think about it, exercise and eat a lot of protein, keep my head up high and a straight posture, like mentioned above. Don't obsess over it, because in my observation, even if you grow an inch or two more, you'll never be quite … Read more

Well, technically, rats would even eat fellow rats, decomposing rats, mice, etc. So in reality, nothing is stopping a rat from eating a smaller rodent, like a mouse.

If you are talking about pets, even if the rat doesn't eat the mouse, it will most likely cause it environmental discomfort and stress.