Lab technician

While one might have thought it strange that he had never encountered this problem before, Mar was correct in that zoan devil fruits do not allow dual-classing between the orders of Mammalia and Aves. So while a hybrid-fruit animal sounds very nice in theory, when you try and mix together biology without fully understanding how it works... it doesn't. And when it doesn't... well, bad things happen.

Actually, a more in-depth explanation can be found many miles away, when a venerable scientist known as Dr. Vegapunk was busy overseeing the results of his latest devil-fruit research.

"So it didn't work out then?"

"No sir!" said the lab technician. "All of our cross-species spliced devil-fruit suddenly failed biologically. Their insides uh... melted, sir."