Final answer:
The Beatles song associated with the 'Paul is dead' rumor is 'A Day in the Life'. This song, along with 'Revolution 9', was at the center of the 1969 conspiracy theory due to its interpreted lyrics and hidden messages.
Step-by-step explanation:
The Beatles song that fueled the false rumor about the passing away of Paul McCartney is 'A Day in the Life'. These rumors of McCartney's death began in 1969 and were further fueled by interpretations of lyrics and album artwork as containing 'clues' to McCartney's supposed demise. One of the most cited songs in relation to the 'Paul is dead' conspiracy theory is 'A Day in the Life', particularly for the line, 'He blew his mind out in a car'. Additionally, the song 'Revolution 9' played backwards has a voice that may be heard saying 'turn me on, dead man', which was purported to be another clue. None of the rumors were true, and Paul McCartney is very much alive.