The clip opens backstage at Late Night with Jimmy Fallon, where Jimmy is walking down the hall on his cell phone discussing a Halloween costume. Around the corner comes Sir Paul McCartney, also on the phone, joking that 'Hey Jude' was originally meant to be 'Hey Dude.' At 0:10, the two collide in the hallway and clutch their necks in shock. When they speak again, they realize they have miraculously traded accents: Paul is stuck speaking in Fallon's American voice, while Jimmy is delighted to sound like a Liverpudlian Beatle.
Rather than helping fix the situation, Jimmy revels in his new Scouse accent, refusing to swap back and spouting absurd phrases like 'SpongeBob SquarePants' and 'YOLO.' Paul grows more annoyed by the second until around 0:52, when he simply slaps Jimmy across the face, immediately popping both of their voices back to normal. The sketch ends on a fun tag as Paul walks away down the hallway, quietly muttering 'Honey Boo Boo' to himself in his restored voice.
It is a quick, lighthearted late-night bit that relies entirely on how game Paul McCartney is to play along with the absurd premise. While accent-swap gags are a staple of late-night comedy, McCartney's deadpan delivery—especially his little coda as he walks off screen—makes the sketch land really well.