Here's why:
* Short vowels are a real linguistic concept. In English, they are sounds produced with a relatively short duration and a higher pitch. Examples include the vowel sounds in "cat," "bed," "dig," "hot," and "cup."
* Rapidly suggests a fast pronunciation. While short vowels are generally shorter than long vowels, their duration can vary depending on the context of the word and the speaker's speed.
It's possible the phrase "rapidly short vowel" is being used in a specific context that is not clear. Could you provide more information about where you encountered this term? Knowing the context might help us understand what is meant.