The bug would have been obvious if the pseudocode had been indented. I'm convinced that a large fraction of beginner programming bugs arise from poor code formatting. (I got this idea from watching beginners make mistakes, over and over again, which would have been obvious if they had heeded my dire warnings and just frickin' indented their code.)

Actually, maybe this is a sign of a bigger conceptual problem: a lot of people see programs as sequences of instructions, rather than a tree structure. Indentation seems natural if you hold the latter view, and pointless if you can only perceive programs as serial streams of tokens.