Optical illusions come in all forms, from mind-bending physiological phenomena to confusing cognitive images, but one variety that doesn’t get nearly enough love is the humble ambigram. While these visual spectacles are often related to calligraphic design, this rotational ambigram example uses numbers to boggle our brains.

When we think of the best optical illusions, often our minds revert to vivid, undulating geometrical designs, but my personal favourites are always the simpler ones (and not just because it saves me a headache). The 23 illusion is a prime example of how visual suggestion can create a crafty illusion, even when we flip our perspective.