I can distinctly recall stuffing a shop rag into the exhaust outlet side of a heat exchanger.
Funny, I couldn't remember taking it out.
The Engine was idling a little funny after start up... hmm, maybe if I goose the throttle a little bit....
Did you know that a scorched, smoldering shop rag can exit a 911 muffler at what seems like 100 MPH?
Everyone makes the occasional mistake (officially termed an "oh *****!")
Learn from it, go back and spend 30 minutes checking all of the orifaces of the motor (you won't feel right until you do.) and move on.
You'll have a nice post for the "admit your stupidity" thread...
AFJuvat