A more thorough explanation:

A speaking demurrer is a type of legal objection that goes beyond the contents of the pleading being challenged. It is an attempt to introduce new evidence or information that is not part of the record. Since demurrers assume that the factual allegations in the pleading are true, speaking demurrers cannot be sustained.

Let's say that a plaintiff files a complaint against a defendant, alleging that the defendant breached a contract by failing to pay for services rendered. The defendant files a demurrer, arguing that the plaintiff did not provide enough detail about the services rendered. This is a valid demurrer because it is based on the contents of the complaint.

However, if the defendant files a speaking demurrer, arguing that the plaintiff actually provided subpar services and therefore breached the contract first, this would not be a valid demurrer. This is because the defendant is introducing new evidence that is not part of the record.