Original: The track was recorded on 8 February 1967, with overdubs on 16 February (bass and vocals), 13 March (brass section), 28 March (backing vocals and guitar solo), and 29 March (animal noises).
Simplified: The track was recorded on 8 February 1967, with overdubs (extra music that's recorded into the song) on 16 February (bass and vocals), 13 March (brass section), 28 March (backing vocals and guitar solo), and 29 March (animal noises).