and where is the illusion at?

dandesign... the two birds are Identical, the gradients make them look different.. yet if you moved them over each other they would blend right into each other (good Luck author)

that's not an optical illusion, after my knowledge

illusion: An erroneous perception of reality

The erroneous Perception.. the two birds are different, the reality, they are exactly the same

Thank you for the help Ernest.

u gave me the meaning of illusion... not optical illusion ) whatever ... lol

optical illusion: A visually perceived image that is deceptive or misleading.

Perceived image is two different birds... the deception is that they are exactly the same... and that's your English Lesson for today young man.. Now go out on the Jungle GYM and have a blast.. hehe

I got to admit, I don't really see an optical illusion either...

I've seen an optical illusion like that before, it was two squares appearently of different colors. But actually they were equal! It's very mysterious, like your work, author! Nicely done, and GL!

It's an optical illusion alright.

An SBS displaying the two birds on a white background might help dispel the confusion.

good luck