And you see what happens to the exhaust after slipping, as shown in that video. Mucks up the tubes and flues. Mark---"and I sand corrected"--great sense of humor.
I am a bit surprised no one has mentioned the "Blue Peter" LNER Peppercorn Clas A2 60532 slip and resulting catastrophe. From Wikipedia: [video=youtube;YjsNbzg1UaI]http://www.youtube.com/watch?v=YjsNbzg1UaI[/video]