A homeless man spending a hot afternoon at the public library grows angry and belligerent. A librarian feels threatened and calls the cops. They'll arrive in 10 minutes.
But what should be done in the meantime? And when police arrive, how do they defuse a potentially violent situation without going overboard?
Ray Hassett, a retired 25-year New Haven, Connecticut, police veteran, has trained both police and librarians on how to deal with these kinds of situations.
His advice to both is similar: Stay calm. Ratchet down the emotions. Do what psychologists call active listening.
"You sound upset," he teaches them to say. "I can hear it in your voice."
It's one technique in a strategy called "de-escalation."
In the wake of a string of high-profile, officer-involved shootings, advocates are calling for more police training, including a greater focus on de-escalation.
It would not necessarily have prevented all of these shootings, many experts say, but learning how to manage volatile emotional situations can help keep things from spiraling into violence.
However, good training is expensive and time-consuming, and critics say not enough police departments are getting it.
And some police organizations are pushing back, saying officers focused on de-escalating are putting themselves and the public at greater risk.
End of reason
Hassett said that when people are emotional, reason goes out the window. And when emotions take over, whether it's suspects, police or librarians, that's when things go badly.
Ex-cop and de-escalation trainer Kevin Dillon said one trick to get emotional people back to a reasonable mindset is to distract them.
FILE - Prince William County, Va., officers collect evidence at a house in Woodbridge, Va., Feb. 29, 2016, following a fatal shooting at the residence during a domestic dispute.
He remembers arriving at the scene of a domestic dispute. The couple were screaming at each other. But Dillon noticed the house was meticulously decorated.
"I said, 'Time out for a second. Who designed that room?' " One person answered, and then immediately went back to arguing.
"I said, 'I don't quite understand that color scheme.' "
The idea is to nudge the anger aside momentarily and re-engage rational parts of the brain. A few questions later, the argument became a discussion, and then a resolution was reached.
"You cannot reason with someone who is that emotional," Dillon said. "You've got to learn to deal with emotion first and then the facts."
Another technique is called motivational interviewing, in which one tells the subject, " 'Give me an idea how to resolve this. I just need some help from you and I'll get out of here as quick as I possibly can.' Most of the time they're going to tell you something you can't do anyway," Dillon said, but it can help get the person thinking rationally.
Officers also have to avoid letting their emotions take over, even when the other person is uncooperative or confrontational.
"When you first feel your blood pressure going up, that's when you reset yourself." He suggested repeating a phrase like, "It's time to go to work," to get the officer back in the right mindset.
Of course, de-escalation isn't always the right approach.
"We're not saying that if somebody comes at you with a knife that you get to know their family," said Officer Tawny Wright of the Fairfax County, Virginia, police, who went through recent training. Officers are expected to protect themselves and the public, she said, and sometimes that means using force.
Training, training, training
Handling these situations well takes hours of training and regular retraining.
But former Seattle Police Chief Norm Stamper said that for the most part, police departments nationwide are doing "a terrible job, frankly, of teaching de-escalation. We're much more likely to provide many, many hours on ... drills to deal with protests or firearms training."
A recent Police Executive Research Forum report found recruits spent an average of 58 hours on firearms training, compared with eight hours on de-escalation. On-duty officers spend 18 percent of their retraining time on firearms on average, compared with 5 percent for de-escalation.
FILE - Police officers pretending to be terrorists receive training weapons during a live counterterrorism demonstration for the 2013 National Homeland Security Conference, in downtown Los Angeles, June 6, 2013.
One reason is money. There's little money left in most police budgets after salaries are paid, according to Jay College of Criminal Justice professor Maki Haberfeld. "Usually when there's sort of a budget cut, the first thing that goes is training," she added.
And out of the 18,000 police departments nationwide, Haberfeld said, "only a handful of the large police forces have academies that can actually provide this simulation."
Furthermore, some of the major organizations representing police officers are not on board.
Responding to a recent bill that would require certain de-escalation training techniques, the National Association of Police Organizations said in a statement, "We believe they are more likely to result in increased officer injuries and death."
The NAPO statement described one tactic as a "time-consuming, unrealistic and paralyzing thought process for officers under threat that also disregards the constitutional legal standard for use of force."
Hassett, the New Haven police veteran, doesn't disagree with those critiques. "They're legitimate if you've never done this type of work," he said.
But with appropriate training and the ability to handle the subject's and the officer's own emotions, he added, "it makes you even safer."