OK this is really frustrating - I've got a screen cap of Fassbender looking at the wriggling worm thing; it looks exACtly like a miniature version of the inner mouth of the xeno, with the teeth and everything. But I'm not allowed to post screencaps; can I email it to someone else who can or something? Or can one of the mods let me post an attachment?...
It's three frames into the shot, around 1:31 of the US trailer if anyone's interested.