President Biden and former President Donald Trump squared off in their high-stakes 2024 election debate rematch on Thursday and the contrast between the pair could not have been more stark, body language expert Susan Constantine tells Fox News.

Constantine says the physical difference between the candidates was noticeable from the moment they both took the stage in Atlanta, and that set the tone for the rest of the evening, with Trump purveying strength and confidence in his mannerisms, while Biden showed a tired and slow demeanor, made worse by his raspy voice, mumbled answers and oftentimes dazed looks.

"I was really concerned because the minute [Biden] walked out on that stage, I felt he [was] not feeling good," Constantine said. "His skin was pale, it was pasty, and he literally looked like a dead man walking."

BIDEN'S 'DISASTER' DEBATE PERFORMANCE SPARKS MEDIA MELTDOWN, CALLS FOR HIM TO WITHDRAW FROM 2024 RACE

Biden looking dazed

Biden looks on as he participates in the first presidential debate of the 2024 elections with former President Trump on June 27, 2024. (Andrew Caballero-Reynolds/AFP via Getty Images)

"It was as if everything were in slow motion," she continued. "His fingers and his lack of illustrators when he was talking, he was like a frozen statue up there on the stage. It really was painful to watch. [Trump] had a more serious demeanor. He didn't make a lot of facial gestures as we normally see him do. He didn't flash his great big smile at anybody. He was very serious when he walked out on the stage, and it really didn't change at all through the entire debate."

Constantine added, "It made Biden look exceptionally weak, and made Donald Trump exceptionally powerful."

Biden's campaign blamed the raspy voice on a cold, but the president's uneven debate performance grabbed the vast majority of headlines from the debate, sparking a new round of calls from political pundits and some Democrats for the president to consider stepping aside as the party's standard-bearer. 

But top Biden allies pushed back against such talk as they defended the president and targeted Trump for lying throughout the debate. 

Constantine says that it was clear that Biden had rehearsed many of his answers and went through his scripted answers very fast so as not to forget his lines. But when he did fail to recollect lines, it tripped him up, resulting in him giving long stares, oftentimes without blinking, which she describes as a "stalker stare." 

"And the minute he forgot a couple of words, it was all over with, right, and then you could see that dropped mouth, and it was that dumbfounded look," she explained. "His eyes would become very open and almost zombie-like. So he had that very flat stare in his eyes."

MEDIA CALLS FOR BIDEN TO WITHDRAW FROM 2024 RACE AFTER 'DISASTER' CNN DEBATE PERFORMANCE: ‘IT’S OVER'

Joe Biden, Donald Trump

Biden and Trump debated in a high-stakes debate Thursday night and a body expert says their gestures told a lot about them. (Getty Images)

She also said Biden had too many cosmetic injections which physically prevented him from making proper expressions.

"He was really way too botoxed out, and that is a real problem because it can create some cognitive issues because when you shut down those emotions through facial effects, it can affect your brain," Constantine explained. "It really almost felt abusive in my opinion, to literally allow him … [to] go through that kind of pressure knowing that he is in this high cognitive decline was to me, almost abusive."

"And it was sad to watch. My heart broke," she added. "I mean, literally, I could have cried watching him try to force these words out the best he could and it was just super hard to watch. The emotion that I felt, of sympathy, of empathy, because he just truly looked pathetic."

Trump, on the other hand, showed discipline and commanded his stage space, Constantine said, adding that the lack of an audience played to Trump’s advantage as it kept him focused on the debate and not distracted.

She said Trump also used his hand movements to convey his messaging. He also expressed his emotions in his face, and said that when he is hurt or attacked, it is noticeable as his face droops downward in a sad gesture.

CLICK HERE TO GET THE FOX NEWS APP 

President Trump speaking and hands showing

Trump used his hands to convey his point in the debate. (Andrew Caballero-Reynolds/AFP via Getty Images)

"He's a big guy with big hands, right? And he captures the attention," Constantine said. "He's very big, and wide and open, and so everything in his gestures and in his movements are big and boisterous. His hands are no more than additional communicators of what he's saying."

Constantine said Trump used a chopping motion when he was serious and used an "okay" sign when he was concentrating on something that was really important. He also gave an "L" sign at ear level which she terms as "listen and learn" while he also moved his hands towards his chest as if he is playing an accordion. 

"[Trump's gestures] are much more rapid and much more commanding, much more intense. But that goes along with his personality so it is in sync with his personality," Constantine said. "We've seen politicians where their gestures are so synchronized and they're so on point that it loses its authenticity. He left that window open so that he was able to gesture, stay within that balance, stay within the frame, connect with the audience, or on camera and not over gesture but just gesture enough to get his point across." 

"Very powerful," she added. 

Fox News’ Paul Steinhauser contributed to this report.