Ttyjukl

In Harry Potter and the Sorcerer's Stone, George convinces Ron that the following nonsensical poem is a spell:

"Sunshine, daisies, butter mellow,

Turn this stupid, fat rat yellow."

But Ron has grown up in a wizarding home, and has presumably heard his parents and siblings using spells all his life. Every other spell, including simple household spells, has a short, Latinate (or occasionally English) incantation like Lumos, Aguamenti, Accio, Wingardium Leviosa, etc., etc. So how could he believe that this poem is a spell? Is there an in-universe explanation for this?

First let me say that I don't believe it is a real spell.

The thing we need to realize is that Ron did not know enough spells to differentiate between fake and real spells. Mr and Mrs Weasley would have used Nonverbal Spells at home.

We also know that Ron blindly trusted his brothers which is normal at that age.

Instance 1:

“So we’ve just got to try on the hat!” Ron whispered to Harry. “I’ll kill Fred, he was going on about wrestling a troll.”

_{^{Harry Potter and the Sorcerer's Stone, Chapter 7, The Sorting Hat}}

Instance 2:

“I’d worked that much out for myself, funnily enough. What happens if you break it, then?”

“You die,” said Ron simply. “Fred and George tried to get me to make one when I was about five. I nearly did too, I was holding hands with Fred and everything when Dad found us. He went mental,” said Ron, with a reminiscent gleam in his eyes. “Only time I’ve ever seen Dad as angry as Mum, Fred reckons his left buttock has never been the same since.”

_{^{Harry Potter and the Half-Blood Prince, Chapter 16, A Very Frosty Christmas}}

Most probably Ron was nervous after all he had five brothers who have been to Hogwarts, he would have definitely been nervous. Knowing Fred and George those guys would have thought it was fun to scare Ron.

Generally younger siblings trust their elder siblings. My brother had me believing in lots of silly stuff when I was a kid!

Who says the spell doesn't work? As far as we know he only tried it on Animagus, which hardly qualifies as an intended target.

Most likely he believed it because it is a real spell. The 'Colour Change Charm' is mentioned in Harry Potter and the Order of the Phoenix, explicitly in relation to the ability to change the colour of a rat:

On the whole, Harry thought it went rather well. His Levitation Charm
was certainly much better than Malfoy’s had been, though he wished he
had not mixed up the incantations for Colour Change and Growth Charms,
so that the rat he was supposed to be turning orange swelled
shockingly and was the size of a badger before Harry could rectify his
mistake.

As to why it didn't work, you can choose from the current answers;

• @Zikato's suggestion that it failed because Scabbers is no ordinary rat seems plausible.




• @Vishvesh's suggestion that Ron's brothers had intentionally taught him a wrong incantation (for their own amusement) also seems pretty plausible as well.




• There are also other spells (eat slugs!) that seem to operate in English.

I think we are forgetting about the changing water into rum spell that is seen later:

Eye of rabbit, harp string hum, turn this water into rum.

This indicates that these more poetic spells do exist or at least thought to exist by more students than just the younger brother of two pranksters.