The Grease: Live costars, who play Kenickie and Rizzo in Fox's live musical telecast, still haven't puckered up to one another – on the mouth, at least.
"Our first time in rehearsal, I'm like, 'Do we just start kissing off the bat? Like, how does this work?' " the 26-year-old told PEOPLE Now on Monday.
"We're like running the show through in our rehearsal space … I was like, 'Oh my gosh! We have to do the whole kissing scene' … so then it comes to our scene, and her and I are, like, sitting there. I started to go in, and I just didn't feel right. So I was like, 'Okay, cool, so we're not doing this.' "
He adds, "So I just kissed her neck."
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PenaVega and Hudgens, 27, are part of the star-studded cast that includes Julianne Hough as Sandy, Les Misérables actor Aaron Tveit as Danny, Carly Rae Jepsen as Frenchy and Keke Palmer as Marty.
Jessie J will open the show with a special arrangement of "Grease (Is the Word)" and Joe Jonas, along with his DNCE band mates, will take the stage at Rydell High's school dance as Johnny Casino and the Gamblers.
Grease: Live airs Sunday at 7 p.m. ET on Fox.