I became an invigilator last year and while doing nothing but watching students fill in their answer sheet, I noticed some 'remarkable actions'. Therefore I decided to take notes and observe more of their behavior. Here they are:
There were students who kept staring at the ceiling or the wall in front of them, trying to retrieve their memory there. Well, it's a common thing to find during examination.
There was this one student who sat right before the invigilator desk and kept looking at me. Whenever I turned my sight on him, I found him staring at me. I don't know why, maybe he found the answers written on my face.
There was also this one boy who put on a sleepy face and finally nodded his head sleeping. I came to his table, asking if he had finished and got 'not yet' as the answer. I just asked him to finish quickly, get out of the class, and sleep in his room.
When running out of idea, some students would secretly turn to their right or left. This is why I prefer to be in a class with familiar students. So it would be easier for me to call them like, "Hey A! don't ask B, he doesn't know either," or "C, don't ask D for the answer, counting zakat is different from counting physics,".
When students got bored of writing down or not knowing the answers (for they had no idea in which part of their brain the said answers were hidden), they began to explore and express their creativity. Not an uncommon thing to find students draw pictures or write graffiti on their question sheet.
The common form of cheating is exchanging question sheets when the considered smarter students submitted their answer sheet. I suspiciously thought this happen several times but said nothing, as I didn't really see it when they did the 'transaction'.
At times, there were students who looked at me constantly with bored face. I knew it from their gestures that they had finished filling their answer sheet and were waiting to submit it then go out of the classroom. I just played dumb and pretended like I knew nothing.
The exam was 90 minutes in duration but most of students finished in 30 or so. The regulation said that they're allowed to leave the room after 60 minutes so it's quite a long time to wait. I just told them to write some poems.
When I was a student, what I did during examination was pouring down all my head's content on the answer sheet. When I got stuck and had no idea what the answer was, I would just hand in the paper to the invigilator and leave the class. For me, no need to force myself to recall something that I don't even remember where in the world I store it. No offense.