(At around 19:30) The rifle on the floor of the hallway changes positions from one cutaway/take to another.
At about 43 minutes, there is a Nelson Institute For Marine Research nameplate on the alien creatures control panel.
Crewman killed by the alien earlier in the hallway is seen later in the control room when same alien takes over control room and makes crew disappear.
Notably during the opening sequence the lines that guide the flying sub are visible.