So Mr Banks writes an advertisement for a new nanny. He wants somebody strict. Jane and Michael write their own, and they want somebody kind. They also say please, and that small word is where our lesson starts. Without it, you are giving an order: “Pass me the salt.” With it, you are making a request: “Pass me the salt, please.”

Mr Banks throws the children’s letter on the fire, but the pieces fly up the chimney. The next morning, a woman comes down from the sky, holding an umbrella and the children’s letter, in one piece again. She is Mary Poppins, and she is “practically perfect in every way”. She is strict, but she is almost never rude. When she wants something, she asks, and the easiest polite request in English starts with could you. “Could you help me?” Those two words turn an order into a question.

When Michael first sees her, his mouth falls open. “Close your mouth please, Michael,” she says. “We are not a codfish.” Even when she tells him off, she says please. Then comes spit spot, which means “hurry up”. That one is an order, not a request.

The children’s room is a mess. Mary sings “A Spoonful of Sugar”, and the toys put themselves away. For a bigger favour, you use a bigger phrase: “Would you mind helping me?”

Be careful with the answer. If the person is happy to help, they say no, not at all, so here “no” means “that’s fine”.

In the park, the children meet Bert, who is drawing pictures on the street. When you speak to a stranger, you start with excuse me. “Excuse me, is this seat free?” It gets attention without being rude.

Mary, Bert and the children jump into one of Bert’s pictures, where penguins bring the tea and everyone dances. When you need permission, you say may I. “May I have this dance?” It is more formal than “can I”, and it sounds very polite.

Later, they visit Uncle Albert, who laughs so much that he floats up to the ceiling, and he wants company. To offer something, you say would you like. “Would you like to join me for tea?”

The answer is easy. To accept an offer, you say yes, please.

And to turn an offer down, you say no, thank you.

Not everyone in the film says yes. Mr Banks does not want to take his children anywhere. But in English, we rarely say a flat “no”. We say I’m afraid not, and here “I’m afraid” means “I’m sorry to say this”, not that you are frightened.

Or we soften it into a warm refusal: I’d love to, but I can’t. You keep the other person on your side, and the answer is still no.

Bert takes the children up onto the roofs of London, where he also works as a chimney sweep, and the sweeps dance in “Step in Time”. Bert is kind to Mr Banks too, and he waits for the right moment. When someone is busy or upset, you start with I’m sorry to bother you.

The words reviewers reach for are the five bonus words above. Frame Rated said no film had felt this magical since Buster Keaton. Many reviewers found the songs fanciful. Critics called it an effervescent and gentle classic. In the Guardian, Guy Lodge described its tuneful cheeriness, and the same Guardian piece praised its sprightly musicality.