“And Your Bird Can Sing (giggling version)” by The Beatles.
The rejected version, heard on the Anthology 2 album, features a vocal track on which Lennon and McCartney are giggling hysterically. The Anthology liner notes states that the tapes do not indicate the source of the laughter. However, given the group’s excessive consumption of cannabis during this period, it is likely that they were under the influence at the time of recording.
(Source: peacethroughmusic, via paulie-my-dear)