When reality turns out to be night and day from a reasonable and logical guess of the

evidence.
The phrase refers the skull of a hippo, which to someone who had never seen the live animal, would

likely assumed it to look like Picture 1, and nowhere near the real animal (see link)

oi66.tinypic.com SLASH bitj45.jpg
Surely it looks impossible that there could be life on Mars. But there may be a hippo paradox!
You may think there's no reason to look further. But don't fall for the hippo paradox.
We all were sure the job would be easy, but it turned out a real hippo paradox.
by Sir Rutherford August 19, 2016
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