Why Does Paul McCartney Call Monkberry Moon Delight a Milkshake?

Monkberry Moon Delight is the name of a milkshake. Paul McCartney says that when the kids were little, they could not always pronounce certain words, and the word for milk was monk. The line he remembers is, Daddy can I have some monk?

He was thinking of a milkshake, so milk became Milk Berry and then Monkberry Moon. Paul McCartney imagined the name and flew off into the lyrics: a piano up his nose, soup and puree, cats and kittens that do not get left behind, and ketchup, ketchup, ketchup. He calls the lines crazy and great, a lot of wordplay from a zany period, and he wishes he wrote songs in that spirit now.

Amy Poehler asks whether Paul McCartney has smoked Monkberry Moon Delight and what he was on when he wrote the song, the question Stella McCartney wanted asked. Paul McCartney says he probably was on something he smoked. In his mind, the title is still the milkshake.