You have the best and most accurate description of a broody hen, @aart, but at 1:30 am I just did the best I could.Broody Trance....clenching?
These are my go-to signs of a broody:
Is she on nest most the day and all night?
When you pull her out of nest and put her on the ground, does she flatten right back out into a fluffy screeching pancake?
Does she walk around making a low cluckcluckcluckcluckcluck(ticking bomb) sound on her way back to the nest?
If so, then she is probably broody and you'll have to decide how to manage it.

