De Vries looks like he's having a lot of fun

the first human that the alien is inhabiting, right at the beginning, just looks like he's having a blast. Just his facial expressions... they always crack me up. I would guess that the actor enjoyed playing the part. I suppose that I would guess that both the actor playing the part, AND the character, were having a blast, in different ways.

Increase the voltage.
But what if he's innocent?
No one is innocent. Proceed.