Sometimes I can tell when my current DM fudges a roll to miss an attack or reduce damage. He has a tell in the specific way he pauses and breathes before announcing the roll, then tries to hurry to the next turn, which only seems to happen when someone is in a life-or-death scenario, but “luckily” survives.
Should I let him know he has a tell? Will it be less fun (or more stressful) for him if he knows I know?
IMHO, the GM’s role is a lot fuzzier than that and is wholly dependent on your specific party’s (and their own!) preferences. I’d say this is simply what you prefer to do as a GM, rather than what a GM should be doing.
Right. I was just expressing my personal philosophy in my previous comment, not prescribing how everyone should play every game. At least, that was the intent.