Arc Warden & his Tempest Double had a mouth displayed in the bottom half of their fishbowl heads, when a voice line was spoken by the respective unit.

As of the recent update (7th December 2018), the update that changed a few things about the loadout and animated portraits, Arc Warden & his Tempest Double stopped using their mouths.

The eyes still show, but the mouth does not.

Before the update: After the update: