John... does not have the best sense motive check when he's not plugged into someone. It's something to do with emotions being something he has less than two years experience with on a personal level and not a 'this lever does THIS thing that makes people make the funny noises'. But he has enough experience, and he spends enough time watching people, and by luck he happens to have recently seen some interactions with the now-departed John Gaius.

Departed, one would believe (as there was no announcement otherwise) due to a graduation.

Hm.

"So... how often do you lie to my face?"