Useless musicological sleuthing of the day…
I like to think that I discovered this—on tour in Spain with the Sixteen, early 1990s:
The numinous opening bassoon solo of The rite of spring, rather than deriving from a folk melody on the elusive dudka, may instead be borrowed ingeniously from the Matthew Passion, 1st violin part in the 2nd orchestra (no.43, not long before Erbarme dich):
with Stravinsky varying Bach’s pitch and rhythms to his taste. Amidst the fray of the crowd scene, investing the phrase with inexplicable care, I always chuckle to myself, “Not a lot of people know that…” [Weirdo—Ed.].