I'm going blind.

You know what's so mind-numbingly difficult, and yet so very, very addictive?

... no, not Sudoku.

Ambigrams. Even more destructively addictive when one has utterly no typography background, a ruler, or a mirror.

Especially when the two words you're combining have all of one letter in common. One. Total. Flippy flippy flippy scribble wheeee!