Every so often someone breaks down. A mother recently left her desk in tears after watching a video of a child being sexually abused. A young man felt physically sick after seeing a video of a dog being tortured. The agents watch teenagers self-mutilating and girls recounting rape.

They have weekly group sessions with a psychologist and the trauma specialists on standby. In more serious cases, the center teams up with clinics in Berlin.

In the office, which is adorned with Facebook logos, fresh fruit is at the agents’ disposal in a small room where subdued colors and decorative moss growing on the walls are meant to calm fraying nerves.

To decompress, the agents sometimes report each other’s posts, not because they are controversial, but “just for a laugh,” said another agent, the son of a Lebanese refugee and an Arabic-speaker who has had to deal with content related to terrorism generally and the Islamic State specifically. By now, he said, images of “weird skin diseases” affected him more than those of a beheading. Nils finds sports injuries like breaking bones particularly disturbing.

There is a camaraderie in the office and a real sense of mission: Nils said the agents were proud to “help clean up the hate.”

The definition of hate is constantly evolving.

The agents, who initially take a three-week training course, get frequent refreshers. Their guidelines are revised to reflect hate speech culture. Events change the meaning of words. New hashtags and online trends must be put in context.

“Slurs can become socialized,” Mr. Allan of Facebook explained.

“Refugee” became a group protected from the broad hate speech rules only in 2015. “Nafri” was a term used by the German police that year to describe North Africans who sexually harassed hundreds of women, attacking and, in some cases, raping them. Since then, Nafri has become a popular insult among the far-right.