This is a video of a dual axis optical illusion of a rotating Lissajous curve (frequency relation 2:3) transformed into 3D space that appears to rotate around a vertical axis when viewed regularly or when moving your head from side to side, but appears to rotate around a horizontal axis if you move your head up and down. *shrug* I don’t know, I have a headache now.

Keep going for the video, which might work better than the gif.

Source: Geekologie – Stop, You’re Hurting My Brain: This Dual Axis Optical Illusion