This slip up occurs at the Joshua computer, right after David escapes from the infirmary and is leaving on the bus. In the next scene, there is a woman walking around the computer who is supposed to be taking readings. She appears to be writing things down on her shiny clipboard paper but...Oops! There's no paper! She's pretending to write numbers down but they forgot to give her a sheet of paper so she's making her pen move back and forth over the chrome on the clipboard.