im sure they feel emotions, small birds feel emotions too, when my cat kills a young bird that just learned how to fly and his parents are near they will chilp like crazy, and not just the moment when my cat killed the bird, no for weeks every day for minutes/hours long they show they are very angry on my cat and want their baby back
Yes, it's probably similar to the emotion people feel when their children are killed. Of course, you don't have to think that way or you'd feel bad about eating cows and pigs and chickens. But yes, animals have feelings. Are mice self-aware..? Not sure. I think the way people define sentience is as this: If it's a life that benefits me by being treated like a person then it's sentient; if it benefits me to inflict suffering on it then it's not a person and therefore not sentient.
The way I define sentience is: If it has a brain then it might be sentient, and if it can recognize itself in a mirror then it's at least as sentient as me, and if it has the same League of Legends rating then it's at least as intelligent as me.