Backwards letters and numbers

Z's favorite toy of late is the magna doodle. In part from noticing the etched ID codes on the windows of our car, he's become fascinated with backwards letters and numbers, and will frequently either draw them backwards or sit in front of the hallway mirror, draw them forwards, and then hold them up to the mirror to see how they look in reverse. Did I mention he's also a huge fan of the percent symbol? This has even become a favorite toy to bring in the car, winning out over (gasp) toy vehicles. He seems to understand this is a bit of a game, often commenting after he draws a backwards letter, "Why did you draw backwards letters?". Tonight at dinner he had some letter cookies, and when I glanced over I noticed he'd flipped all of them over on his plate as well, saying "It's backwards letters and numbers!"