The idea of not being able to unhear something might be an aberration of the correct use of English, but it's actually a real thing. Play this 50-second Soundcloud, an audio illusion, and you'll see what we mean. "Your brain is always using prior information to make sense of new information coming in," the commentator says, and that applies to listening to music - although sometimes dubiously, especially when it comes to misheard lyrics. Hearing "bald-headed women" instead of "more than a woman" on the Bee Gees song is you being daft and picking up on something that isn't actually there; a different kind of illusion.
What follows are 10 examples of quirks in songs - recording errors, missed cues, imaginative samples, and so on - that are there and you may have not noticed before. But now we've pointed them out, there's every chance you'll never be able to listen to the tracks in the same way again, and for that we apologise.
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1. James Blunt comes in four bars early in You're Beautiful
We'll begin with a well-known one, but one that's a bit more confusing than it initially seems. Click on the above video and you'll notice that James Blunt's life is so brilliant he comes in four bars early to tell us, then he repeats the opening lyric in the correct place. And if you're thinking, "How did I not notice that before?" it might be because you've only heard the song on the radio. The blooper was removed on radio edits, but that didn't stop "Weird Al" Yankovic from spoofing the false start in his parody of the song, You're Pitiful.
2. John Bonham's squeaky drum pedal on Led Zeppelin's Since I've Been Loving You
The truth is that if we listed all songs on which you can hear a squeaky kick drum pedal, you'd never be able to listen to huge swathes of rock music again. So let us ruin just one song for you - Led Zeppelin's Since I've Been Loving You. Hear the squeak? It's really annoying, and now you'll never unhear it.
Amazingly, the band didn't notice it at the time. "The only real problem I can remember encountering was when we were putting the first boxed set together," said Jimmy Page in 2003. "There was an awfully squeaky bass drum pedal on Since I've Been Loving You. It sounds louder and louder every time I hear it! That was something that was obviously sadly overlooked at the time."
3. The aerosol spray hi-hat in Theme from S'Express
Not all things you can't unhear are errors, though. In the 1980s, when sampling became popular, musicians took to sticking unusual elements in their songs. In the BBC documentary Synth Britannia, for example, there's wonderful old footage of Depeche Mode recording the sound a pebble rolling down a metal window frame, which they then sampled and turned into a percussive noise on their 1983 Construction Time Again album.
And while in hip hop and electronica, sampling often meant clipping out sections of old records, plenty of dance producers took a more organic route. We mentioned this in a recent BBC Music article, 10 of the weirdest things used to make great music, but it's good fun, so we're telling you again - the hi-hat on S'Express's classic acid house hit, Theme from S-Express, is the sampled sound of an aerosol can being sprayed.
4. Bowie barks an order at Mick Ronson in The Jean Genie
RCA Studios, New York City, 6 October 1972: David Bowie and his band, which includes Mick Ronson on guitar, are recording the soon-to-be-classic track The Jean Genie. There are far too many pages on the internet discussing this, but what seems to happen is Mick comes in early on the first chorus (at 37 seconds, above), forcing Bowie to tell him to "get back one" or possibly "get back on it". They decide to leave the order in the final mix.
5. Kurt Cobain's crummy-but-cool solo on The Man Who Sold The World
Sticking with Bowie, sort of, here's Nirvana playing the title track of his third album at their much-admired 1993 MTV Unplugged show. Skip forward to around 2:48 and you'll hear Kurt slip really badly into his guitar solo. It's a mistake that he corrects, and it doesn't matter. Much like the famous "zih zih zih zih zih" ad-lib in the Afrika Bambaataa & Soulsonic Force track Planet Rock (a result of forgotten lyrics), it gives the song personality, and it was a live performance anyhow.
Notice also the "woo!" at 22 seconds from a crowd member, and never not notice it again.
6. Strawberry Fields Forever is two takes spliced together
Beatles songs are stuffed full of great quirks, like the subtle off-mic swear in the background of Hey Jude and the more noticeable dropped tambourine in I'm Looking Through You. And in the days before digital editing, options for producers to splice different takes of songs together were limited. They had to be clever, and skilled, as George Martin was.
Strawberry Fields Forever is two versions edited together at the 60-second mark. You'll need to have very good musical ears to notice the cut, but it is there. It was John Lennon who suggested to George that he combine two different recordings, to which George replied: "There are two things against it. They are in different keys and different tempos. Apart from that, fine."
He sped up the first version, slowed down the second, creating a near-seamless match.
7. The hiss on Miles Davis's Kind of Blue album
This is definitely the one we feel most guilty about telling you about. Across all of Miles Davis's classic Kind of Blue album, there's a noticeable hiss (as indeed there is on many recordings from the 1950s). We're really sorry. And it's even more noticeable on that lovely vinyl copy you have.
8. The headphone bleed on Christina Aguilera's Beautiful
Here's another one to file under 'cool anomaly that only adds to the song'. Check the end of the above snippet - you can pick up the backing track that Christina Aguilera can hear in her studio headphones bleeding into the actual recording.
Mixer of the track, Dave 'Hard Drive' Pensado, was once asked about the bleed. It's fair to say that he rather likes it: "The song was about being beautiful and honest in EVERY way. That bleed is honest. It was one of the most honest vocal performances I had EVER heard. It was actually the scratch vocal. Christina still had the lyrics in her hand. She truly has THE GIFT. So I tried to make the mix as honest as I knew how. I studied Imagine by John Lennon and used that as a guide. To me the bleed at the end was HONEST. When I took it out, I missed it. It sounded too clean and contrived."
9. Sting sits on a piano at the beginning of The Police's Roxanne, laughs
10. Those panting noises during the guitar solo on Guns N' Roses' Rocket Queen...
If you're still reading this, move onto the next item on the internet immediately. Because no one needs to know this and, once again, we're just very sorry for telling you if you didn't already know. Those panting noises during the guitar solo on Guns N' Roses' Rocket Queen from Appetite for Destruction? Over to Steve Thompson, an engineer of the album: "Axl [Rose] wanted some pornographic sounds on Rocket Queen, so he brought a girl in and they had sex in the studio. We wound up recording about 30 minutes of sex noises. If you listen to the break on Rocket Queen it's in there."