Yes, there is often a period in which there are enoughmicroorganisms to make you sick but not enough to be detectable bythe look, taste, or smell of the food. But eventually those thingswill be affected.
One very early warning that usually occurs well before thereare enough microorganisms to make you sick is the surface of thefood develops a "slimy" feel. It is still usually safe to eat suchfood when this just begins, especially if you cook it as themicroorganisms are still only on the surface of the food. But becautious! Note: this does not apply to ground meats and choppedfoods, if they get "slimy" throw them out immediately!