Rabbit-Duck Illusion

The rabbit-duck illusion is an ambiguous image which may be both perceived as a rabbit and a duck. This optical illusion was first published in Fliegende Blatter, a humor magazine, in 1892 and was popularized by Joseph Jastrow, an American psychologist. It has been suggested that the animal first perceived is correlated with sociological and psychological factors that is why it is classified as a cognitive illusion.

For instance, people may see the rabbit first on April, the month of Easter, while they may see the duck first from August to October, the peak of bird migration.