Nick Reiner may have experienced a moment of elation while eerily smirking during his arraignment at a downtown Los Angeles courtroom Monday.

Body language expert Susan Constantine exclusively spoke with Page Six after Nick pleaded not guilty in connection to the stabbing deaths of his parents, Rob Reiner and Michele Singer Reiner.

“There is a really interesting smirk where his head goes down and then he smiles,” Constantine said, adding that he was “trying to conceal his emotions” by tilting his head downward.

Constantine classified his expression as “a form of leakage” called “duper’s delight.”

“‘Duper’s delight’ is when a person gets a sense or rush or enjoyment,” she said. “You will see that it’s almost like a sinister smile and it kind of leaks out at the most inappropriate moments.”

Constantine believes Nick was exhibiting a “form of enjoyment” in that moment, but that he was also trying to hide his emotions.

“It was an unconscious smirk of a sense of enjoyment or elation or excitement,” she said.

Once Nick became “consciously aware” that he was smirking, Constantine said he quickly “changed his behavior.”

Constantine, whose book “How to Spot a Liar in 7 Seconds or Less” will be released in 2027, also speculated that the “pulsating” in Nick’s jawline and the lines on his forehead reveal that there is “a lot of tenseness.”

“His forehead shows a lot of worry,” she said. “His eyes show paranoia and fear — high levels of it. An intensity level of it.”

As Page Six previously reported from Nick’, 32, ‘s arraignment, where he was seen on camera wearing a brown jumpsuit and had his hands shackled during Monday’s arraignment.

The hearing marked the first time Nick was seen in the Los Angeles courtroom. The “Being Charlie” screenwriter had sunken eyes and a shaved head.

He sat with a stoic expression alongside his attorney, public defender Kimberly Greene.

The judge asked if he was willing to waive his rights to a speedy preliminary hearing, to which Nick replied, “Yes.”

His next court appearance is scheduled for April 29.

Nick, 32, was arrested and charged with two counts of first-degree murder with a special circumstance of multiple murders after his parents were found stabbed to death in their Brentwood home on Dec. 14, 2025. Rob was 78 and Michele was 70.

According to the LA County Medical Examiner’s Office, the “When Harry Met Sally” director and Michele died from “multiple sharp force injuries.” Their death was ruled a homicide.

Nick appeared in court that month wearing a suicide prevention smock, though he wasn’t wearing one during his second hearing in January.

Ahead of that court appearance, Nick’s lawyer, famed criminal defense attorney Alan Jackson, suddenly quit. Jackson said at the time and he and his team had “no choice but to withdraw and ask to be relieved.”

Nick — who is facing a maximum sentence of life in prison without the possibility of parole or the death penalty — is being held without bail in solitary confinement at the Twin Towers Correctional Facility in Los Angeles.

Rob and Nick allegedly got into an argument at Conan O’Brien’s Christmas party the night before the Hollywood icon and Michele were killed.

However, a close friend of Rob told Page Six that Nick and his parents were getting along great just weeks before their tragic deaths.

Nick has been in and out of rehab for drug addiction and was diagnosed with schizophrenia before his parents died.

Nick’s siblings, Romy Reiner and Jake Reiner, have kept a low profile, though they have been slowly returning to normal life after losing their beloved parents.