Vowel team OO can also say a short /oo/ or /ů/, as in book.  When decoding vowel team OO, you can start by saying the short /oo/ sound and then listen for any changes when naturally spoken, as in “book”.

/ů/, /ů/, /ů/, book

The  /ů/, as in “book”, can be said and remembered by thinking of the sound “oof”, as if someone bumped you in the stomach. The sound is quick and soft, not long and not stretched out.