Great finding this juvenile barred owl at the local swamp early in the morning.
Owls have specially designed feathers that make them noiseless so indeed the mouse doesn't hear it coming. However it is most unlikely the mouse dies during the attack. Instead it is carried to a branch where it is pulled apart alive. I watched a Sharp-shinned Hawk do that to a Red-bellied Woodpecker. What most likely happens is the victim goes into shock.