Commenters on the blog pointed out a pretty glaring problem in the experimental setup; their control boxes contained tape with no writing on it at all, which op

Commenters on the blog pointed out a pretty glaring problem in the experimental setup; their control boxes contained tape with no writing on it at all, which opens up the possibility that package handlers were responding to the presence of text, rather than the content of it. A human handler might be concerned about terrorism or something, and an OCR might just get confused. Commenters suggested labeling controls with a neutral word, and also trying labels such as "Allah" for comparison.