This modulation happens within the first 10 seconds (though you should listen to this whole song, and whole album, because they are both awesome):
A conventional four-bar arpeggiated introduction (I – vi – ii – V, strongly establishing a key area) gives way to a wailing vocal that enters a full step above where you’d expected to be.
Rather than intensification (there’s barely anything to intensify), the purpose here seems to be disorientation, and through disorientation, the bold announcement of a new sound that turned out to be a seminal change in pop music; Sir Paul McCartney has gone on record saying that without Pet Sounds, there would have been no Sgt. Pepper.
-Matthew Wrather from Overthinkingit.com