the saliva carries along, and they swallow it, their prayer does not become invalid; because it is impossible to avoid this. If one keeps a morsel in their mouth and does not swallow it, it is disliked; because it distracts them from the humility of the prayer, the remembrance, and the recitation within it, but it does not invalidate it; because it is a minor action, so it resembles the case where one holds something in their hand. And Allah knows best.