What is the cause of excessive screaming for mild pain in elderly people?

Excessive screaming: I would wonder if the pain isn't really mild. If the person has dementia sometimes they will seem to overreact to stimuli that wouldn't bother other people; it is part of being confused and possibly afraid of whatever is happening. If they aren't suffering from dementia then they might overreact for reasons that all of us overreact; being neglected, a need for attention, underlying anxiety etc.

Low tolerance: A lot of elderly people as they age lose tolerance to anything that irritates them including pain. When they are aggrevated they tend to be less inhibited about what it is that is bothering them, and speak( or scream) like if in pain, the person in line at the grocery store, well, you know what i mean by now!