[tomsmeding]

zUck https://en.m.wikipedia.org/wiki/Near-open_central_vowel

bOOk https://en.m.wikipedia.org/wiki/Close_central_rounded_vowel

[vxNsr]

Must be a midwestern accent thing, I don’t pronounce book, “boooook” (as in what a ghost with a cough says)

[smolder]

Book/nook are not as in boo/goo, but they're also not the same as in buck/Zuck. This is not a Midwestern thing. I can't recall ever meeting a native US english speaker for whom these vowel sounds weren't distinct. Probably in some accents they blur together.

[saltcured]

Rather, I think some may be rhyming Zuck with buck which does not rhyme with book.

Edit: oops, smolder said the same thing but I was reading a stale page without the reply...

[dmvdoug]

Here are some pairs of words to show they don’t rhyme:

Pluck / took

Duck / rook

Suck / shook