[SlowToady]

Regarding the use of "esta" (accent on the a), it is because the condition, dead or alive, of the dog changes, or rather, changed. "El perro es muerto" would indicate the dog was always dead and NEVER lived, hence a static state, whereas "El perro esta (con accento) muerto" indicates (as Paco mentions) that the dog was once alive and is now dead --a dynamic state.