When the Rat Pack performed, in addition to songs and jokes, there were often some celebrity impressions thrown into the mix. Dean did pretty good impressions of Clark Gable and Cary Grant, and Frank played around as James Cagney. But the real impressionist in the group was Sammy, who did some spot-on imitations, both talking and singing.
But when it was time for the impressions, Frank and Dean pretended to make it hard for Sammy, by inviting him to the microphone and then cutting him off. They're seen needling Sammy this way during the Rat Pack benefit show filmed in St. Louis that's available on DVD.
When Sammy did his impressions, they included great imitations of singers like Tony Bennett, Vaughn Monroe and Nat King Cole, with the crowning touch being his singing impressions of both Dean and Frank as they looked on.
Today, you'll see impressions of Frank, Dean and Sammy performed by Rat Pack Impersonators.