How do you spell the sound of opening mouth?

There isn't a single spelling that perfectly captures the sound of opening your mouth. The sound can vary depending on the context:

* "Ah" is a common spelling used for a simple, open-mouthed sound.

* "Aah" is another option, often used to express surprise or pain.

* "O" can be used for a wider, more exaggerated open-mouthed sound.

* "Ooh" can be used for a more drawn-out, slightly hesitant open-mouthed sound.

Ultimately, the best spelling will depend on the specific sound you want to convey.

You could also use descriptive words like "gaping," "yawning," or "stretching" to evoke the action of opening your mouth.