This is a product of good photo-manipulation. It looks so realistic that it seems the eye really popped out from the egg. I think it is somewhat difficult to differentiate the parts which are added afterwards and the ones which are in the photo originally. Despite that, I found that it is essential to make the source of light consistent within the same image like the direction of the light source and the hardness of the it.
For example, at the iris of the eyeball there is a square of reflection of light the photo-manipulator made to simulate light hitting on the original image. It is a little bit too hard for me though, I think these are the details needed to be paid attention to when manipulating images.
This is another manipulated image from deviant art. I think the concept of water as the candle fire is an idea which is done before. However, I think the way this photo-manipulator put the water droplets on the candle cap shows how light hits on them. It becomes harder when the water droplets are on a curved surface. Attention has to be paid on how the light changes when the light hit the droplet and how it bounces back when it hits the candle cap. It requires more observation on subject matter.