More than 100 years after it was first sketched, an image still depicts either a rabbit or a duck – depending on how quickly and creatively your brain works.

Recently making rounds on social media is the rabbit-duck illusion, which first appeared in 1892 in a German magazine known as Fliegende Blätter (Flying Leaves), carrying the caption “Which animals are most like each other?”

The sketch rose to popularity when philosopher Ludwig Wittgenstein used it as an example of two ways of seeing the same thing.

It was then used by an American psychologist named Joseph Jastrow in 1899 to illustrate his study on perception.

Jastrow’s research delved on how fast one can spot the second animals and how quickly the participant can change his or her perception of the drawing, switching between the two creatures.

The suggestion: the faster one can do this, the quicker his or her brain works and the greater the creativity is.

The results of this test, however, appear to change at various times of the year. During Easter, for instance, people tend more toward seeing a rabbit first. In October, on the other hand, seeing the duck first seems to be more common.

This ambiguous illustration shows how the brain is receptive to visual tricks – although it could get really confusing to explain why.

In a TED-Ed video titled “How Optical Illusions Trick Your Brain,” educator Nathan S. Jacobs explains the biological workings behind the human perception of a 2D drawing, depending on the orientation of the picture.

“[Optical illusions show the] brain’s job as a busy director of 3D animation in a studio inside your skull,” he said, adding that it is reserving cognitive energy and creating a world instantly with tried and sometimes deceiving tricks of its own.

Spending this cognitive energy as efficiently as it can, the brain uses assumptions about visual cues to form “a tailored, edited vision of the world,” Jacobs added.

While one probably knows now why she sees both the rabbit and the duck, it may take a while to figure out what seeing one of the two animals first say about her personality.