According to the New York Post, a source close to Depp confirmed that the gesture by attorney Benjamin Chew in the Fairfax, Virginia, courtroom was a "celebratory acknowledgment."
"Amber mentioned an ex of Johnny's that clearly she felt was not supportive of him, which couldn't be further from the truth," said the source, which seemed to be a reference to Moss' potential to help Depp's case.
The experts said that Heard mentioning Moss on the stand could give her ex-husband's team an opportunity to quell a rumour that he pushed Moss down a flight of stairs when they dated in the 1990s.
This possible slip-up from the Aquaman actress occurred on Thursday as she told the jury about a March 2015 fight in which she punched Depp in the face over fears that he was going to shove her sister Whitney down stairs.
Heard said she "instantly" thought about the Kate Moss incident, which provoked Chew to turn and fist-pump.
Generally, alleged misconduct that is unrelated to a specific accusation within a case - such as this rumoured one - isn't permitted to be dished out by lawyers during a trial.
However, Heard mentioning Moss could open the floodgates for Depp's attorneys to call the supermodel in as a witness to speak on the allegation, experts further told the outlet.
"[Moss] is still allegedly friends with Johnny, and her testimony wasn't allowed to come in before because it wasn't as relevant," said Mitra Ahouraian, a California entertainment lawyer.
"[Moss] is still allegedly friends with Johnny, and her testimony wasn't allowed to come in before because it wasn't as relevant."
Halim Dhanidina, a criminal defense attorney and former California judge, also agreed that The Pirates of the Caribbean star's team could now also try to use "the Moss mention to their advantage."
"Johnny Depp's team is going to argue that they should be permitted to call her to debunk any rumor about Johnny Depp pushing [Moss] down stairs," Dhanidina said.
Dhanidina also said that Heard's side could also counter that Moss reference and explain that it was meant to detail Heard's "state of mind" when she hit Depp.
Still, Depp's side will likely cross-examine Heard about the Moss reference.
Dhanidina further explained that the judge on Depp's case, Penney Azcarate, has "a lot of discretion" on whether or not to continue on and let Moss testify.
During Depp's 2020 defamation trial in the UK, Heard had also made allegations that the actor had shoved Moss down a flight of stairs.
Speaking on the same fight that involved her sister, Heard told the British court the following during that time: "I remembered information I had heard [that] he pushed a former girlfriend — I believe it was Kate Moss — down the stairs. I had heard this rumor from two people, and it was fresh in my mind."
Should the judge in the ongoing trial allow this allegation to come into play, it could also open up the floor for Depp to bring forth previous accusations of misconduct against Heard.
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