Especially something vague like “say any words” and especially when you don’t understand in much depth the utility of the task or trust very deeply the person who asked you to do it. People often say things they don’t mean literally. Not you, but they don’t know that.

Give them a finite time. They’re not believing you when you say “forever until I say so” so try “for thirty solid minutes or until I stop you.” It’s really hard to keep doing something indefinitely without any encouraging feedback.