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The branding ceremony took place in 2017 inside a house near Albany, where female members of the so-called cult Nxivm held an initiation for the newest member of an ultrasecret sect.

That member, Lauren Salzman, testified on Monday that she knelt and said, “Master, please brand me, it would be an honor, an honor I want to wear for the rest of my life.” Then she was held down on a massage table as someone used a cauterizing pen to etch the initials of Keith Raniere, Nxivm’s leader, into an area near her hip.

“It was the most painful thing I have ever experienced,” Ms. Salzman said during her second day of testimony in Mr. Raniere’s sex trafficking and racketeering trial.

Ms. Salzman also testified on Monday about how women who joined the clandestine sect, called The Vow or D.O.S., made secret commitments to become lifelong “slaves” to Mr. Raniere.