What's a side remark called when it's meant as something sarcastic or secretive?

What do you call the gesture when someone makes a sarcastic or parenthetical side-comment? It's usually something related to the original comment that's said quietly to someone else, sometimes sarcastic, sometimes secretive. In movies, the person puts their hand at an angle near their mouth and usually raise an eyebrow if it's sarcastic. I know there's a name for that kind of gesture -- anyone know what it is? I found "side remark" in the thesaurus but it doesn't have any words that indicate something quietly shared away from or about the source comment.

Solution 1:

Snide

adjective

3 : slyly disparaging : insinuating < snide remarks >

Snide remarks

Snide remarks are the kinds of things people say with a sneer on their face. When you leave a movie theater and your friend says, “I can't believe someone was actually paid to write that screenplay,” he's being snide.

Another possibility, which doesn't have the malicious connotation is to "interject"

interject

vb (tr)

1. to interpose abruptly or sharply; interrupt with; throw in: she interjected clever remarks.
2. to come between; interpose

interjection

noun

1. the act of interjecting.
2. something interjected, as a remark.
3. the utterance of a word or phrase expressive of emotion; the uttering of an exclamation.
4. Grammar: any member of a class of words expressing emotion, distinguished in most languages by their use in grammatical isolation, as Hey! Oh! Ouch! Ugh! Any other word or expression so used, as Good grief! Indeed!