Feist, as quoted there, does not appear to touch upon that issue.
At issue there was the copying of only factual material from a phone book.
Creators of copyright traps contend that, as they are not facts, they are original content and subject to copyright.
I believe the courts have ruled that is not so, but apparently Feist isn’t the case where that happened.
Early Control Data Operating Systems had the words “COPYRIGHT CONTROL DATA CORPORATION” early in the source code of the system. But rather than being a comment, they were stored as actual literal data. Then at various places scattered throughout the code, those storage locations were used in instructions. For example, an instruction JMP chr[7]-chr[6] (=“G”-“I”) translates to JMP -2, for a jump 2 lines back, a tight loop instruction. But it only works correctly if those storage locations contain “IG”. Enough of those were included that changing that copyright notice made the OS fail in strange & wondrous ways.
And they take no extra CPU time, because this is translated by the address decoding logic as the instruction is loaded. And they were quite hard to locate in several thousand lines of assembler code, especially back in punched card source code decks.
I don’t think that would be original enough to be eligible for copyright.
Further to the Mr Ed story, There was a famous April fool on British TV about spaghetti trees. It was presented on a serious news programme called Panorama by Richard Dimbleby, the senior presenter at the time.
It featured film of a family from Ticino in Switzerland carrying out their annual spaghetti harvest, with women carefully plucking strands of spaghetti from a tree and laying them in the sun to dry.
Many people were fooled and years later, there were still some who believed that it must be true because it was on Panorama.
Broadcasting Magazine sold mailing lists of licensed radio and TV stations. In my job I sometimes bought one. I know they had at least one fake address in Washington, DC which was where there headquarters was. It was also where I lived so I knew there was no such station. I suspect the address, a PO box, was received right in their offices, as the real address and the fake one both shared the same zip code.