How do you know if a blackbirds eggs are addled?

Addled blackbird eggs typically appear discolored, misshapen, or have a cloudy appearance when compared to healthy eggs. Additionally, if they are left unattended for an extended period without signs of hatching, or if they emit a foul odor, these are strong indicators that the eggs may be addled. Observing the behavior of the parent birds can also provide clues; if they abandon the nest or show signs of distress, it may signal that the eggs are not viable.