1 - Gene Kelly with Donald O’Connor
2 - Gene Kelly with his stunt man, Russ Saunders
3, 4 - Gene Kelly with Debbie Reynolds
Look at how differently they move. Gene is a machine, while Donald is much looser, a hoofer. Neither is better than the other, but clearly shows the difference in training. Gene was all about rehearsing until it’s perfect and you follow me, while Donald feeds off of who he’s dancing with and reacts to changes.
On the BBC2 special they talked about this, about how Gene never looked at Donald - he just expected Donald to match him because they rehearsed it and Gene was the point person. He locked it all down in his head before hand. Stanley Donen would tell him afterward if it didn’t work. Donald would constantly check their feet because that was his style. This gif really shows that.