Galen Fott writes to Mark Evanier and says...

"My version is better. I moved Groucho's backwards lines to where Groucho speaks, and the same for the other two. In doing so, it becomes obvious that this is how it was accomplished originally, that the backwards lines we hear are actually the brothers speaking live in the studio, and that the sound engineer later broke this into four pieces (not two, as Stan Baker did), reversed them, and spliced them back in."

See what happens when you actually put effort into something like this?