...it's been a while, so my memory is hazy, but I seem to recall catching a documentary-type show once, where there were multiple tanks in a lab, one containing an octopus, and I think fish of some description in another. The "other" tank kept consistently and mysteriously coming up short of head-count in the mornings. A camera was set up, and it caught the octopus actually crawling up the side of its tank, crossing the floor, and going into the other tank for a snack; then returning home.

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It is hard to convey five-dimensional ideas in a language evolved to scream defiance at the monkeys in the next tree. -- The Science of Discworld III: Darwin's Watch, by Terry Pratchett, Ian Stewart & Jack Cohen