Sir Paul McCartney has revealed where he finds inspiration to finish writing some of his songs - in the toilet.
The former Beatle, 72, disclosed how he goes about songwriting - and why he avoids penning tracks about sex - in an interview with Q magazine.
And he also hinted that his US wife Nancy Shevell was left unimpressed by his latest collaboration with rapper Kanye West, because of the song's use of "the n-word".
McCartney, who is famed for being one of the greatest living singer-songwriters, told how he begins writing with any "first line" even "if it's rubbish...to get started".
Asked whether he had ever felt shy about playing someone a new song, Sir Paul told the magazine: "Shy, embarrassed, yes, if it's not finished."
The star, who penned his first song when he was 14, added: "The trick is to go off on your own and finish it.
"Go into the toilet - toilets are good. Separate yourself."
While Wings' 1972 hit Hi Hi Hi was banned by the BBC for its references to sex and drugs, McCartney a dmitted: "Sex is something I prefer to do, rather than sing about.
"Hi Hi Hi was from a period when everybody was getting stoned and having sex....I suppose singing about sex is not really in my genre."
He added: "I can be angry but I can't find a natural way to put it into a song. It's the same with sex...."
McCartney has been collaborating with West, most recently on All Day, which the hip hop star performed at the Brits.
The musician said: "I think he mentions the 'n' word about 40 times. It's controversial, I know, especially with the climate in modern-day America.
"It really shocked Nancy (McCartney's wife), because she'd been to school with a lot of black kids and been immersed in that experience."
McCartney also revealed that he now believes in star signs and that he attributes his songwriting talents to the fact that he is a Gemini.
"There are two sides to Gemini. And if you listen to my stuff there are two sides to some of it - Ebony and Ivory, Hello Goodbye...so I never used to believe all this, but now I'm thinking 'Maybe there's something in it'."
He said: "I've never been into the zodiac before.... but just recently I've started to think about this wheel of life, and how, at certain points in the year, people get thrown off... and are born."