To the extent that America still has a collective cultural memory, it’s comforting to have the happy stuff to hold on to. And it’s depressing to arrive at a juncture that forces us to let some of that stuff go. For much of its eight seasons, “The Cosby Show” (which ran from 1984 to 1992) was foolproof happiness, and the primary source was Bill Cosby. Now, at the close of a depleting, inconclusive criminal trial, we’re back to reckoning with what to do with him and whether it’s still possible to laugh at his comedy.

The moment that Americans would probably cite as peak “Cosby Show” bliss happened in 1985, during the second season, when the Huxtable family lip-synced to Ray Charles’s “Night Time Is the Right Time,” for the 49th wedding anniversary of Cliff Huxtable’s parents. You forget how much Theo leans into the opening verse, from the stairs, and how Sondra, Denise and Vanessa are barely there as Raelettes.

But that’s only because what everybody remembers, what everybody still melts over, is wee Rudy’s pretending to belt the climactic Margie Hendrix part. (“Bay-bay!” Hendrix screams, “Bay-bay!”) All the comedy comes from the incongruity of a snaggletoothed kindergartner mimicking, with all her might, a grown woman’s yearning. She didn’t fill Hendrix’s shoes — who could? — but her trying to suffices as a definition of joy.

Rudy became the show’s secret ingredient. When a scene called for authentic precocity, she would blurt out something, grin or just say her kid-chauvinist pal’s nickname: “Buuud.” Cuteness like that helped, in 1986, make the actor who played her, Keshia Knight Pulliam, the youngest-ever Emmy nominee. Cuteness like that made Rudy a textbook definition of “little sister.” Her percolating feminism eventually made her more than cute. If anything about television remains sacrosanct, it’s Rudy Huxtable.