Lewisohn writes that, after the final piano chord, "John Lennon suggested that they insert a high-pitch whistle especially for dogs, 15 kilocycles, to make them perk up.”
Within that piano chord itself, you might hear something more mundane. It was produced by John, Paul, and Mal Evans simultaneously pounding an E major chord on three adjacent pianos, and letting it ring out for 53 seconds in the take that was used. But a minute is a long time to ask for absolute quiet in a jam-packed studio, and "one can hear a rustle of paper and a chair squeaking," Lewisohn writes.
The ultimate Beatles Easter egg was in the run-out groove of the original LP release. Following the piano chord and dog whistle
comes some gibberish designed to make anyone with a non-automatic turntable go insane as the same nuttiness repeated over
and over. For decades, fans have slowed down those few seconds to try to make out what the voices are saying, and they
usually come up with something obscene. But engineer Geoff Emerick says those efforts at deciphering are in vain.
"The decision to throw in a bit of nonsense gibberish came together in about 10 minutes. They ran down to the studio floor
and we recorded them twice," he says in The Complete Beatles Recording Sessions. "They made funny noises, said random things;
just nonsense. We chopped up the tape, put it back together, played it backwards and threw it in...There was no hidden meaning.”
The run-out groove madness was deleted on subsequent pressings of the LP after the '67 first edition, but restored
for the 1987 CD, as was the dog whistle effect.
In the alternate version of "Day in the Life" found in the Anthology series, you get to hear Paul swear. After he sings, "Everybody spoke and I went into a dream" instead of the intended "somebody spoke," he blurts out, "Oh, s---!" Some sources claim that in the officially released version, you can hear him snicker at that same mistake, even though the gaffe had been overdubbed.
Finally, a note from the orchestration of "A Day in the Life" was used as a sort of proto-sample on "Revolution #9" from The White Album.