Heard returned to the witness stand in Virginia where jurors are considering duelling defamation claims by the former spouses.
The pair married in February 2015 and took their honeymoon on the Orient Express train in July of that year after Depp finished filming the fifth "Pirates of the Caribbean" movie.
Under questioning from her lawyers, Heard said the couple argued about whether Depp should drink during the trip. She said they had a loving relationship when Depp was sober but that he often turned violent when drinking or using drugs.
In a sleeping car on the train, Heard said, Depp slapped her across the face and repeatedly slammed her body against a wall. He then took his shirt off and wrapped it around her neck, she told the jury.
"That's how I woke up the next morning," Heard said. "I woke up with it still around my neck and a giant knot on the back of my head."
The court was also shown photos of Amber Heard’s scarred arm at a 2015 red carpet event which she said was caused by a violent incident involving Johnny Depp and a vodka bottle.
“Those are scars that I obtained as Johnny was strangling and assaulting me on a countertop in Australia,” Ms Heard told the court.
Jurors were shown a photo taken at a New York City premiere for the independent movie When I live my life over again on 15 April 2015.
Ms Heard said the event took place soon after an incident in early March in Australia where she said “Johnny held me down on the counter tops and my arms were cut on the glass in that attack”.
Another photo from a second red carpet event was shown to the court, revealing several scars on Ms Heard’s left arm as she brushes her hair from her face.
Ms Heard said that she had tried to cover the scars with makeup but they were “a bit harder to cover as they’re rather fresh”.
The "Pirates of the Caribbean" star testified earlier that he never hit Heard and argued that she was the abuser in their relationship.
Depp, 58, is suing Heard, 36, for $50 million, saying she defamed him when she claimed she was a victim of domestic abuse. Heard has counter-sued for $100 million, arguing that Depp smeared her by calling her a liar.
Heard also told the court that Johnny Depp was hallucinating and that his sobriety had completely collapsed in the final months of his marriage.
Heard said it was the couple's teacup Yorkshire terrier Boo that messed the bed and that it had a history of bowel problems ever since it had accidentally ingested Depp's marijuana.
“Absolutely not,” she said about the alleged prank. “I don't think that's funny. I don't know what grown woman does. I was not in a pranking mood.
"My life was falling apart.
"I was at a crossroads in my life. I'd just been attacked on my 30th birthday by my violent husband, with whom I was desperately in love and who I needed to leave.
"It was not really a jovial time and I don't think that's funny. Period. That's disgusting."
Earlier, Johnny Depp appeared to scoff as an audio of Amber Heard calling him “Junkie Johnny” was played in the court in the former couple’s multi-million-dollar defamation trial.
Heard is being sued by Depp for $50m for implying he abused her in a 2018 Washington Post op-ed.
Although she didn’t name him, he claims her allegations impacted his ability to work.
Heard will continue giving testimony today. She has already spoken extensively about her troubled relationship with Depp and detailed alleged physical fights.
The jury will also hear from Whitney Henriquez, Heard’s sister, and actor Ellen Barkin, with whom Depp had a brief relationship in the 1990s.
Giving evidence last, on May 5, Amber Heard burst into tears and struggled to finish sentences during her testimony at a US defamation trial as she described how Johnny Depp had allegedly violated her with a bottle.
The actress said that during a violent argument with her former partner, Mr Depp had held her by the throat and smashed glass at a property in Australia in March 2015.
Mr Depp is suing the Aquaman star for libel over a 2018 article she wrote in The Washington Post which his lawyers say falsely implies he physically and sexually abused her while they were together.
The actor has denied all accusations.
Describing the alleged 2015 incident during the second day of her evidence, Ms Heard told jurors that following a struggle they had ended up on a counter top and she had felt “pressure on my pubic bone”.
“I felt this pressure, I thought he was punching me. I saw his arm. I could feel his arm and it looked like he was punching me,” she said, her voice breaking.
“I felt pain and pressure on my pubic bone.
“I don’t remember what I said, I just remember being really still…looking around the room, all the broken bottles, broken glass.”
Ms Heard’s lawyer Elaine Bredehoft asked the actress to clarify the graphic details of the alleged penetration, which she did.
“I was heartbroken (but)…the discomfort I was feeling afterwards paled in comparison with how scared and shocked I was.”
The actress said Mr Depp had also broken a phone at the property “into smithereens”, ripped her nightgown off, and screamed at her repeatedly that he would “f****** kill” her.
Jurors heard that the morning after the alleged incident Ms Heard had discovered “incoherent” messages written in navy-blue and brown paint, and food smeared on the walls of the property.
She added that pieces of raw meat wrapped in a silk gown she owned had been hidden in various locations around the property.
“It was bizarre,” she said.
She later added that she had been “destroyed” by the incident and had feared leaving to go home because Mr Depp might harm himself.
“I was worried we couldn’t come back from what had happened…that there was no way we could turn it around,” she said.
During another incident she said Mr Depp had held her into a pillow-top and she had feared she could die as she struggled to breathe.
The court was also shown several pictures of Ms Heard displaying injuries she had allegedly received during the violent altercations with Mr Depp.
Earlier, she detailed to the court other instances of “disgusting” verbal and physical abuse she had allegedly suffered at the hands of the actor.
The court heard the relationship had become a “constant battle” and that Mr Depp had taken particular issue with her professional relationship with actor James Franco, whom he “hated”.
They were also played audio clips of an incident on a plane in May 2014 in which Ms Heard alleges she was kicked in the back by the actor, who became so intoxicated he “howled like an animal”.