Here's why:
* The vowel sound is short: The "i" in "lizard" makes a short "i" sound, like in "sit" or "fish".
* The vowel is followed by a consonant: The "i" is followed by the consonant "z".
* The vowel is not at the end of the word: The vowel is not at the end of the word, which is another indicator of a short vowel sound.
Therefore, the vowel sound in "lizard" is a short vowel sound.