Here's why:
* Short vowel sound: The vowel sound in "mug" is short and quick, like the sound of "uh" in "cup."
* One syllable: "Mug" is a single syllable word, which often indicates a short vowel sound.
* No vowel digraph: The vowel sound in "mug" is represented by a single letter "u," not a combination of letters (digraph) like "ou" or "ai".
Therefore, "mug" fits the criteria for a short vowel word.