Another thing to note, since it's filmed in slow motion, Zhora's chest wound makeup appliance actually separates from her chest (hence why her chest wound magically disappeared) and flops around as she breaks through the second window...
it's because it's like deckard is watching. it's horrible to watch, we hardly want to see it as if it's a stuttered sort of replay. it's not that it disappears, it's that we're watching it more than once. why should deckard feel bad about killing something that is "not human?" this is one of the ways in which Ridley Scott refers us again to the theme of what it means to be human.