Jay Leno rolled footage from a high school production of "Grease" in which Smith played a rather static-looking Kenickie.
The "Babble-On Begins" creator then jumped up to show Leno his signature Kenickie hip swivel, which hadn't gone down too well with his mom at the time.
"My mother’s like, 'Never do that again,'" he laughed. "And I said, 'Because it’s dirty?' And she says, 'No, 'cuz you look pregnant.'"
"The Tonight Show" airs weeknights at 11:35 p.m. ET on NBC.
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