The professor was sure that this picture was crooked in its frame.
"Look at that writing", he said, "You can see it's on a slant". Sure enough, he was right. (See comparison with true horizontal, right)

The professor kindly volunteered to give tha painting a "bit of a wash-down" while he had it out of the frame to reset it. Doing so, revealed some surprising details

It was about this time that we started to wonder if there wasn't something a bit "fishy" about the professor's work.

At least the writing isn't slanted now.