The secret bit of code in the core of the old Mac OS

I was trying to recount the following for a co-worker, but I couldn't find a reference to it anywhere.

I had heard some years ago that there was a part of the core code in the old Mac OS (pre-OS X, afaik, and not sure what version) that, according to legend, supposedly no one on the development team at Apple at the time knew what that code did. I assume it was compiled code, or it may have just been some random-looking binary data, and I guess it just wasn't obvious how it was being used. When someone attempted to remove (or modify?) it, things stopped working. So, they left it in place and moved on.

I know this story doesn't sound that interesting at first. After all, what developer hasn't run into code at some point they didn't understand right away? But, the interesting part of this was that it was stated that no one on the team knew why it was there and just left it like that. It has been a number of years since I heard this story and now can't seem to find more detail. Does anyone else remember? Thanks!