> "from here we can state that, obviously..." He suddenly stops, slowly turns the head down, keeps mumbling "so we can obviously...". He slowly walks in the room, trying to catch the thought, then leaves the room... Some minutes pass. Then he comes back, with head up, widely open eyes and confidently continues - "Yes, this is completely obvious - so from here we can easily get the following conclusion."

I had a lecturer who did this! With the only difference being he didn't leave the room, he would just stand there speechless with a poker face and then - 0.5-1 minute later - he'd say "well, this is obvious".

SUDDENLY, during the exams he expected us to explain the obvious.