He is trying, in spite of the obvious flaws in his plan,
to run a Voidt-Kampf test on his best friend.
He's seen Blade Runner probably one too many times at this point
and has begun to doubt the humanity of other people.
It's not that he thinks his friend might be a robot
-that would be absurd, obviously-
but he keeps noticing the way other people tick over differently to him
the way they describe the sky with words like
'blue' and 'clear'
when he prefers words like 'Pearl'.
He's not sure that other people see the same things he does,
has started to mistrust the refraction of lenses
to tell us all the same truth about the world
and, if he's being honest,
thinks other people might all just be a trick that god is playing on him.
So he runs his test
and even though his friend is humoring him he's starting to wonder
if maybe he shouldn't be running the test on himself.