London: A US-based artist claims to have cracked the Leonardo Da Vinci "zoo" code -- a 500-year-old mystery -- after he discovered hidden animals in the famous Mona Lisa portrait.

Ron Piccirillo, the amateur oil painter and graphic designer based in New York, believes that animals, including lion (top right), an ape (top left) and a buffalo (bottom right) are visible if one turns the Mona Lisa onto its side.

According to him, he followed a series of instructions set out by the artist Leonardo da Vinci to decipher the image and claims his discovery cracks open the meaning of the work, painted in 1519, a mail reported. Piccirillo claims to have found similar hidden images in works by other Renaissance painters such as Titian and Rafael. It was when he turned the painting on its side that he first noticed the lion's head.

He said: "Then I noticed the buffalo and I thought, 'Oh my God'. Then I realised I was really onto something. I just could not believe what I was looking at. I realised, 'this is what I've been looking for'."

Piccirillo also said he had found either a crocodile or snake by following the instructions of da Vinci's journals.

Looking at the painting from a 45 degree angle from the left, the path that runs in the scenery behind the Mona Lisa appears almost serpentine. This was supposedly where the angle of the light was best and led to least amount of reflection.

From a diagram in da Vinci's journals which explained this, Piccirillo called it the "D-point". The instructions also called for the viewer to put their eyes on the same level as the horizon in the painting.

From this he was able to make sense of the line in the passage about how to paint envy which reads: "Make her heart gnawed by a swelling serpent", as there is such a creature emerging from her right breast.