about the verb "sham" (to smell): is it a doubled verb or a required verb?

The Shaykh : It comes with a kasrah or sometimes with a dammah. Sometimes it comes with a dammah if the verb is defective with a waw, like "ad'u" (I call) or "ighz" (you raid).
The student: ... .

The Shaykh : Yes, write what is in it. The defect of the taa is a dammah. Write the taa with a dammah.

The questioner : ... .

The Shaykh : What?

The questioner : ... .

The Shaykh : One does not say "sham."

The questioner : "Sham" is a past tense verb.

The Shaykh : No, for "sham" we say: "shumma" (it was smelled), just as "shudda" (it was tightened) is a past tense verb, whereas "shud" (tighten) is an imperative verb, like tightening a rope.

The questioner : ... .

The Shaykh : Yes.

The questioner : ... .

The Shaykh : Okay, I say: We heard the recitation of the lesson today. The lesson today. May Allah reward you with good. He reads with his two eyes, looking at it. Ah.
The student: ... .

The Shaykh : Yes, that is fine. The kasrah is not corrected; the kasrah is cancelled. Yes, no, no. We heard it. As long as five have not completed it, do not wait.

The questioner : ... .