The egg was supposed to have a super facehugger: it would implant one host with a queen (it tried Next, then went for Ripley) and then to protect that host it would also implant something else with a warrior (the ox, but in the final cut a dog). When Fox screwed things up they didn't use the super hugger and went with a normal one. I imagine for the assembly they couldn't do new shots of the super and used what they had.