In the comics, one of the first lifeforms to come in contact with Doomsday on Earth is a bird. It lands in his hand and he kills it. In the show, a bird flys in Doomsday/Davis' room. When the camera pulls away, we see the dead bird on the desk
Davis's immortality as Doomsday is true to the comics because Doomsday in the comics could regenerate every time he is killed and adapts so that he could not be killed the same way. The only way Doomsday could die is to completely obliterate every part of him - which means he is immortal, but not invincible.
The poster for "Lobo - Road Trip" seen in the basement of the Talon at the end of this episode references a DC character who at times is a hero, at times a villain, and always a bounty hunter who rides a special motorbike that allows him to travel safely through space [and travel through time, occasionally].
After Lex and Davis leave to go play, Feathers is seen dead on the desk, assuming Davis killed it. In "The Death of Superman" comic book storyline, when Doomsday first comes into contact with Earth's creatures, a bird lands in its hands. Doomsday then kills it by crushing it.
The flashback of the first meteor shower actually uses footage from both the first and second meteor showers to hit Smallville.