When news breaks about a dangerous situation, it’s natural to wonder what one might have done in a similar scenario: Tried to help? Been courageous? Perhaps made things worse? Running into burning buildings and shielding others from active shooters may be the sort of dramatic situations that come to mind. But far subtler opportunities to intervene on behalf of fellow humans come up more regularly than one may recognize — right in the grocery checkout aisle, for example, when witnessing a tense parent-child interaction. That’s the sort of scene Nancy Weaver and her colleagues at St. Louis University’s College of Public Health and Social Justice have been helping others around the region visualize and then learn to respond to in positive, practical ways.