That thing that is popping out of the guy's back? It is a proto-alien known as the Neomorph. It is supposedly very similar looking to the official alien, but it is even more animalistic and reportedly very translucent and freaky looking...and it is just barely visible in the trailer. Watch closely when the grenade is fired through the curtain. You can see...well, something
recoil from it towards the bottom of the screen. It is very quick and blurry as hell to spot, but it is there. To add to the ick factor, they not only pop out of backs, but out of throats as well. So...that's...better, maybe?