* Roll: The vowel sound in "roll" is a short "o" sound, similar to the vowel sound in "hot" or "lot".
* Ghost: The vowel sound in "ghost" is a long "o" sound, similar to the vowel sound in "go" or "boat".
Think of the difference between "roll" and "role" (a part in a play). "Roll" has a short "o" sound, while "role" has a long "o" sound.