"This is the most interesting part of digging into the mind shafts of the people that experienced the era."
This is #2 of the three newly-discovered Horrors in the old gradebook I came across yesterday. And THIS (finding the Horrors) is far and away the most interesting part of digging around in old gradebooks!
I wish I could persuade myself that my student was trying to evoke a complex image here. Possibly, yes, she wrote "digging" and decided to follow the metaphor.