In his later years, Charlie Chaplin made a film called Limelight that belatedly teamed him up with Buster Keaton.
It bowed out with a poignant musical number in which the two old rivals took to the stage, stoking the embers of past glories and stirring memories of the way they were.
I was reminded of this scene while watching Righteous Kill, a leaden police procedural thriller that's notable only for the fact that it stars Robert De Niro and Al Pacino - two titans of the American Method school, together at last. They deserved a better showcase than this.
De Niro and Pacino play Turk and Rooster, a pair of jaded New York cops on the trail of a serial killer.
The killer appears to be targeting pimps and child abusers - the urban scumbags who beat the system.
Suspicion eventually falls on the curmudgeonly Turk, much to the horror of Rooster, who regards his partner as a role model.
There are stand-offs and shoot-outs, stake-outs and fist fights. But the plot feels perfunctory, as though it was penned in haste after the players signed on.
The inevitable gun-toting finale is not so much a twist as a kind of arthritic waddle, a sloughing off of awkward baggage.
These two actors performed separately (split by a generation) in The Godfather: Part II and then squared off briefly over coffee in Michael Mann's Heat.
But Righteous Kill is the first film to feature them as a double act - and don't think it doesn't know it.
Significantly, director Jon Avnet chooses to open with an extended, swooning montage that pits his players in macho competition. We watch them duelling on the shooting range, pumping iron on adjacent benches, and tussling over a chessboard.
Were it not for the demands of that pesky plot, this montage would have probably gone on ad infinitum.