All the dinosaurs which had taken refuge in the Amazon rain forest, and the frozen mountain regions of the great white north could come out of hiding and dominate the planet once again.
Dogs would line the vacant streets, waiting for something to chase.
Birds would have to go back to building their nests without gum wrappers, twist ties, and yarn.
The udders of dairy cattle all over the world would explode.
Little capuchin monkeys holding out little red hats would be ignored, leaving them feeling unloved.
Cats would not notice, until they got hungry.
Fish would flourish, and so then, grizzlies and eagles.
Transports would land, ready to take humans to an enormous planet rich in resources, and finding nobody here, grab a few guinea pigs for pets, and leave.
Cows would no longer feel a need to hide the fact that they can talk.
Birds would no longer be able to line up on power lines, and would have to reintroduce themselves to trees.