Do not use moldy bread. Mold is not a flavor. It’s a green, fuzzy betrayal that will send your Thanksgiving to the emergency room. Throw it away. Respect the bread enough to let it die with dignity.
Also, don’t use bread that’s rock-hard like a museum artifact. If you can’t cut it with a serrated knife without chipping a tooth, it’s too far gone. You want stale, not fossilized. The line between “perfect for stuffing” and “use it as a doorstop” is very thin.
Finally, never leave uncovered bread near your cat. I once did this, and my cat, Sir Fluffyton, used the cubes as hockey pucks across the kitchen floor. Cat hair is not a spice. Trust me on this one.