Is it a common phase for 3 year olds, or is it a sign of giftedness at 3? I don't remember my older daughter being aware of death so young, but my DS3 is very curious about it right now and not in a scared or morbid fashion--just very matter-of-fact about it.
His grandma was talking about a turtle she had as a child, and he asked her what happened to it. Overprotective mother that I am, I started into a long story about how turtles live a long time, and how it was probably living happily in a pond somewhere. He thought about it for a minute, then said, "No, I think it died." Cracked us both up.