Slate talks to the Silver Fox about how the sausage is made:

Slate: During that LSD trip, Roger sees Don in the mirror and later he sees Bert on a dollar bill. Did you have direction from the script as to how to respond in those moments, or did you need to come up with on your own sense of why he was seeing those things and how he would react? 

Slattery: That was all in the script that Scott Hornbacher directed. That was a very difficult sequence to put together. And there were things that were cut--some jokes. I think they were smartly cut, because there were a lot of gags, and I think the whole trip was less jokey in its final form, less joke-filled than it was on the page. Which is smarter, I think, because it would have been just a series of gags. Obviously we have a very short time to put all this stuff together. 

There were a lot of special effects they have to lay over--a gag where Roger's cigarette shrinks, and then the mirror stuff. Looking down at the bill and then looking at her in the cab--you know, it's all on a stage in the car with a green screen, and them talking us through the beats--"Now look at the bill, now look at her." And it was all really specifically laid out--the music coming out of the vodka bottle was there in the background. I took the cap off, and they played the music. I put it back on, and it would shut off. So they do everything they can to help you out.