Why do animals not always scream out in pain when they are very hurt or eaten by another animal?

I know that sometimes animals do, but they also a surprising amount of time just stay completely silent which I'm curious about.

I live ina central part of my city with much greenery around, and we have foxes. Two times I've seen a fox snatch a hare. Both times the hare has struggled, but it hasn't made any death screams or anything.

If you also watch animal documentaries with lion grabbing gazelles and such, they also often stay silent through it all while struggling.