1: The scene did not originally exist at all.
But as McDermitt explains, showrunner Scott M. Gimple then decided a proper introduction was in order.
Scott Gimple told me that Heath was just there in the script that they wrote, says McDermitt.

Credit: Gene Page/AMC
And they thought, what better character to put there than Eugene!
Not only that, but here comes interesting tidbit No.
Allow McDermitt to explain: We actually had a few alternate lines that we had shot.
[Heath] said, Deanna put you on guard duty?
Its been more than a few ticks.
We had a couple of alternate lines there.
He said, I was walking by and she asked to use the restroom.
Shes been gone a while.
I suspect shes dealing with an unannounced visitor much like myself.
Hers of the female variety.
I was like, Yes, lets do that!
McDermitt and Gimple apparently discussed various options for Eugenes retort.
At first Gimple was throwing some alternate lines at me.
He said, Do you want to do this?
Do you want to do that?
And I said, That might be too much, but I kind of love it.
And he said, Oh, its not enough!
It will be perfect.
So we shot that thinking that was going to happen.
Which was still great.
It turns out that wasnt the only TMI line Eugene uttered.
I think there was a diarrhea joke at one point.
Why not, right?
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