«اِللِّسَانْ عَدُوِّ الْقَفَا»

The saying treats speech as the cause of a slap: a careless word may stir an opponent or superior to strike the speaker on the back of the neck. The nape is figurative, the body part that receives the blow, not a separate subject of the warning.

The warning concerns speech and its immediate consequences, not anatomy or the body in general. The blow may come from an offended listener who reacts at once, or from an authority figure punishing disrespect; both share the caution that careless speech invites prompt retaliation. It is distinct from the related horse saying.

Speakers use it as a cautionary remark, usually addressed to someone whose careless or provocative words have caused trouble, or as a general reminder before a risky conversation. It suits informal advice about guarding one's speech in tense company; avoid it where a direct, literal warning would be clearer.