"We kind of do what you do! We always kind of... as soon as the audience, as we meet them, we just start dancing," McCormack, 55, reveals as videos of the cast dancing play in the background.
"And then we start gyrating all over each other and feeling each other's bodies," 50-year-old Messing shares. "... It's just we can't help it."
Mullally, 59, credits the dirty dancing to the show's casting directors.
"When they cast this show, they cast four humpers. All we do is hump each other all day long," Mullally jokes. "... It's sad. It's really sad. We're like grown-up people."
In addition to the daily dancing, the cast also has another way they prepare for each taping.
"We do have a ritual, it's very theater-like because we all have a theater background," Hayes, 48, shares. "So Deb started it from the pilot on that we all get together and we do a little prayer, and we still do the prayer every single show."
"And nobody else knows it," Mullally adds.
"We're not going to say it right now because we're taking it to our graves," Messing claims before McCormack jumps in, jokingly revealing the prayer to be "Please, God, let this be funny."
Mullally also uses her Ellen appearance to marvel at how far the cast has come since the show first premiered back in 1998.
"When we started the show I was living in an apartment in West Hollywood two blocks from [Ellen's] and I had $200 to my name," Mullally, who plays Karen on the sitcom, says.
"And I had loaned her that $200," McCormack jokes.
"I'll never forget, we were shooting the pilot in front of a live audience and Sean made his first entrance, said his first line, and the audience went bananas. They went crazy for him," Mullally continues. "... They'd never seen him before, it was just legitimately so funny and brilliant. I'll never forget it."
"And it's been a law of diminishing returns ever since," McCormack, who stars as Will on the series, quips.
Now, more than 10 years since the series debuted, the show is heading into its 10th season; the second since it was granted a revival last year. While on Ellen the cast gave short descriptions for what their characters are up to in the season premiere, which debuts Oct. 4 at 9 p.m. ET on NBC.
Messing's Grace is running for political office, Karen is a "no good, dirty rotten scoundrel," and Hayes' Jack is planning his wedding when the show picks up. It's Will who may have the funniest plot point, though!
"Will leaves. He was being Grace's lawyer and now he's going to teach law. Because that's hilarious," McCormack jokes. "It's a gay Welcome Back, Kotter is what it is."
Watch the video below for more on Will & Grace's new season: