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"The Simpsons" is arguably the greatest animated series in history. Similarly, "Cheers" is almost certainly one of the greatest live-action sitcoms of all time. But what would happen if these two worlds met? That question was answered briefly (and hilariously) once in 1994 when Homer Simpsons stumbled into the most famous bar in TV history. Yet, during his trek there, a certain voice was notably absent from the proceedings -- namely, that of Kelsey Grammer, who has played Sideshow Bob since the earliest days of "The Simpsons."

Grammer, of course, also played Frasier Crane on "Cheers" before eventually headlining the very successful spin-off "Frasier." Nevertheless, he didn't lend his voice to the crossover in question. It happened during the episode "Fear of Flying," which aired as part of "The Simpsons" season 6. The main plot of the episodes involves Homer being awarded...