John: Hey, man. What's that noise?
John: What do ya say?
Paul: I say, ruff!
John: Do you know any more?
Paul: Rowooooorrrrrowf! Ahhh-hahahahahaa!!
John: You've got it! That's great! You hit it! That's it, man! Woop! That's it! You got it! Ha ha ha!
John: Don't look at me, man. I only have grandchildren.
Paul: Ha ha hoo ha ha hoo etc.
John: Okay. Quiet, boy! Quiet!
Paul's barking like a dog, and John's quieting him down (as you would a pet), tossing a Lennonish joke in the middle. That's about all the "meaning" there.
The real meaning is that even in 1968, they could still goof around hysterically with each other and be cheeky enough to keep their improvisations in the finished version.