I came across this scene in Harry Potter and the Order of the Phoenix. Ron is trying to say something, but I have no clue.
Unfortunately, Ron's mouth was packed to exploding point again and all he could manage was "node iddum eentup sechew"
Ronald Weasley, Chapter 11, Order of the Phoenix
Nearly Headless Nick was upset at something Ron said, considering it mockery of his death:
‘Terrified? I hope I, Sir Nicholas de Mimsy-Porpington, have never been guilty of cowardice in my life! The noble blood that runs in my veins –’
‘What blood?’ asked Ron. ‘Surely you haven’t still got –?’
‘It’s a figure of speech!’ said Nearly Headless Nick, now so annoyed his head was trembling ominously on his partially severed neck. ‘I assume I am still allowed to enjoy the use of whichever words I like, even if the pleasures of eating and drinking are denied me! But I am quite used to students poking fun at my death, I assure you!’
Therefore Ron was probably saying something like: "No, I didn't mean to upset you." (Or possibly "mock you").
As @seumasmac noted in the comments, it's easier to parse Ron's statement if you divide the words this way: no/de iddu/m een/t/up sech/ew = "no, I didn't mean to upset you"
And as a commenter said, this Quora answer agrees.
This book discusses how the garbled sentences in this chapter were translated into other languages:
It goes “Node iddum eentup sechew” (189). Ron is telling Nearly-Headless Nick that he didn't mean to upset him. The Spanish, French and German translations of this passage show that the translators “got it” and were able to present the puzzle to their readers.
