EVERETT — A man who gave his girlfriend a fillet knife for Christmas was treated at a Seattle hospital for stab wounds the following day.

Detectives with the Everett Police Department’s Major Crimes unit believe the woman, 18, stabbed her boyfriend and slit his throat with the knife Thursday evening. Police impounded the Toyota Tercel where the confrontation took place.

Bleeding from the neck, the Shoreline man, 25, walked into a grocery store in the 3000 block of Everett Avenue around 7:45 p.m. before collapsing onto the floor, Everett police officer Aaron Snell said.

Employees provided immediate medical assistance and called 911, Snell said.

The man had an 11-inch gash across his throat that included a cut to his trachea. He also was stabbed in the chest and had cuts to both hands, court papers said.

Police arrived to find a customer applying a piece of cloth to the man’s neck.

The suspect was found lying on the floor by his feet, court papers said. She was covered in blood.

She told police that the man is her boyfriend and that they live together.

The woman alleged that the man had threatened to hurt her several times, including on the drive home from a fishing trip they took Thursday. She told police that he told her he would “cut her up and throw her in the river,” court papers said.

She said she acted out of fear when she unsnapped the sheath and stabbed him.

From his hospital bed, the man denied making any threats.

“He said he had no idea why she would do it,” police wrote in a report. “He said he did not make any threats to her. He said it happened in an instant.”

The woman was booked into the Snohomish County Jail for investigation of first-degree domestic violence assault.

The man first was taken to Providence Regional Medical Center Everett but was moved to Harborview Medical Center because of his injures. He was listed in stable condition.

Eric Stevick: 425-339-3446; stevick@heraldnet.com.