I took this photo of my kid playing with his blocks the other day, and when I realized it reminded me of something, well...I had to make this.
@[email protected] I guess I felt the credit was implicit, given that I mentioned being reminded of something, and that anybody at all familiar with xkcd would probably recognize the lettering, if not the exact text (both of which I obviously copied and pasted).
Still, it's possible people mistook this as entirely original, which wasn't my intention. And it never hurts to be explicit.