We have a tan rat and on the inner sides of his eyes i think there is blood?

my brother's rat, raticus (we have three rats, two are mine and one is my brother's. they share the same cage.) she has blood on the inner thing of her eye, like not IN the eye, but where it connects. idk how to explain. where people tend to find "eye boogers," so anyway. do you think the red stuff is eye "boogers" or blood?