Here's why:
* Short vowel sounds are typically quick and sharp. The "oo" in "shook" is pronounced like the "u" in "cup" or "sun," which is a short vowel sound.
* Long vowel sounds are typically drawn out and longer. Think of the "o" in "go" or "hope" – those are long vowel sounds.
Let me know if you have any other words you want to check!