Justin Long hummed a familiar tune in front of the artist of it.
There have been lip syncs and covers of "Shake It Off," but the song is so catchy that even Justin Long can't help but hum along, no matter where he is.
The Lookalike actor heard the song at a recent Knicks game, and as he told HuffPost Live, "It's one of those songs that really gets in your head, really crawls in there."
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So when it "crawled in" his head, he began to hum the tune -- but didn't realize he was doing it with the song's artist, Taylor Swift, right next to him.
"And of course she heard it," he said. "And she was like, 'Oh,' and sort of started laughing, and I was so embarrassed."
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He swears he wasn't trying to impress the pop star and never would have done it at all had he been "conscious" that she was right there.
But even Swift was quick to remind him, "That's the whole point of the album!"
The 1989 album's catchy songs made it no.1 on the Billboard 200 with 1.287 million copies sold in just in its first week.
Can't get enough of "Shake It Off?" One Direction can't either. Watch what the boy band told ET about what they do to the song.
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