Mordents
Mordents and turns are common embellishments for Lennon [...].
— Walter Everett, The Beatles as Musicians, Vol. 1 (2001), p. 72
Many Beatles songs written by John Lennon contain mordents in the vocal melody: a note briefly ornamented by an adjacent scale degree before returning to the original note. He often places them near the ends of phrases where they're followed by a downward resolution to the tonic.
These ornaments are common in many styles of music, but they distinguish Lennon from his bandmates Paul McCartney and George Harrison, who use them much less often. Lennon himself uses them most in his R&B-inspired songs from the early '60s.
There are also conspicuous vocal mordents in "Do You Want To Know A Secret," which was sung by Harrison but written by Lennon.
References in later music
The Beach Boys
It was clear that the Beach Boys were listening to the Beatles in 1964; [...] [Brian] Wilson adopted Lennon's mordent in such songs as "Don't Worry Baby" and "You're So Good To Me."
— Walter Everett, The Beatles as Musicians, Vol. 1 (2001), p. 276
Single falsetto note
[Little Richard] would say, 'I taught Paul everything he knows'. [...] I had to admit he was right.
— Paul McCartney, Twitter (2020)
Paul McCartney sometimes sings a single note in falsetto, in imitation of Little Richard who did it before him.
