Bert: Speaking of names, I know a man with a wooden leg named Smith.
Uncle Albert: What's the name of his other leg?
George Banks: Kindly do not attempt to cloud the issue with facts.
Mary Poppins: We can't have them gallivanting up there like kangaroos, can we?
Mrs. Banks: I'll try to do better next time.
Mr. Banks: Next time? My dear, you've engaged six nannies in the last four months. And they've all been unqualified disasters.
George Banks: I suggest you have this piano repaired. When I sit down to an instrument, I like to have it in tune.
Mrs. Banks: But, George, you don't play.
George Banks: Madam, that is entirely beside the point!
Mary Poppins: Supercalifragilisticexpialidocious.
Mary Poppins: I beg your pardon, are you ill?
George Banks: I hope not.
Mr. Banks: Just a moment, Mary Poppins. What is the meaning of this outrage?
Mary Poppins: I beg your pardon?
Mr. Banks: Will you be good enough to explain all this?
Mary Poppins: First of all, I would like to make one thing quite clear.
Mr. Banks: Yes?
Mary Poppins: I never explain anything.
Mrs. Banks: As a matter of fact, since you hired Mary Poppins, the most extraordinary things seem to have come over the household.
Mr. Banks: Is that so?
Mrs. Banks: Take Ellen, for instance. She hasn't broken a dish all morning.
Mr. Banks: Really. Well, that is extraordinary.
Mrs. Banks: But you're always saying that you wanted a cheerful and pleasant household.
Mr. Banks: Winifred, I should like to make a slight differentiation between the word cheerful and just plain giddy irresponsibility.
Mary Poppins: Our first game is called Well Begun is Half-Done.
Michael: I don't like the sound of that.
Mary Poppins: Otherwise titled Let's Tidy up the Nursery.
Michael: I told you she was tricky.
Mrs. Banks: I'm sorry, dear, but when I chose Katie Nana, I thought she would be firm with the children. She looked so solemn and cross.
George Banks: My dear, never confuse efficiency with a liver complaint.
Answer: Most likely a variation on the "inexhaustible bottle" magic trick which has existed in various forms for hundreds of years - it relies on different chambers holding different liquids, and air holes in the bottle being covered or not change the pressure and allow the desired liquid to flow out. As the scene is one continuous shot with the entire bottle visible, this seems most likely - the air holes could be on the side away from the camera, with Julie Andrews repositioning her thumb for each colour. More info here: https://en.wikipedia.org/wiki/Inexhaustible_bottle.
Jon Sandys ★