Hear-Wear was about a patent on hearing aids. The patent was being reconsidered by the Patent Office, and the independent claims had already been held unpatentable.

But a dependent claim further added an element about a wire coming out of the hearing aid:

Claim 3. The at least partially in-the-canal module for a hearing aid of claim 2 [of the Hear-Wear patent] wherein said insulated wiring portion is terminated by a plurality of prongs that provide a detachable mechanical and electrical connection to an audio processing module.

Most people call this a plug: a plurality of prongs (those two things at the end) that provide a detachable mechanical (you can plug and unplug it) and electrical connection (electricity flows across the prongs) to an audio processing module (whatever you plug it into, like your computer).

It is hard to believe that a patent could be granted for adding a multi-pronged plug to a well-known invention. “Every purchaser of electrical devices in the United States for the past 50 years or more is familiar with multipronged electrical connections,” wrote the lone dissenting judge in Hear-Wear. But the two judges in the majority would have none of that. As they said, the Patent Office “cannot accept general conclusions about what is ‘basic knowledge’ or ‘common sense’ as a replacement for documentary evidence for core factual findings in a determination of patentability.” Proving this patent obvious, according to them, required paper documentation.