Rails metal call order

I was really mystified today trying to figure out how to bump up the response in Rails metal. The default metal generator generates something that looks like the following:

I had mistakenly changed it to 500 and didn’t realize why the app completely broke. It turns out that Rails itself uses a 404 code in the metal response to go up the call chain to the next metal:

So if you want to return from the metal, just send back a 404.