The letters Alef, Hey, Vav, and Yod can sometimes be “quiescent,” that is, silent under certain circumstances.  video
When an alef occurs without a vowel, then it is quiescent as in חַטָּאת.

Quiesce, Elide, and Assimilate
Went out for a stroll about half past eight.
Quiesce was seen, but never heard.
Elide disappeared without a word.
Whatever happened to assimilate?
A footprint dagesh points to his fate.