"I have no mouth and I must scream"

[Tiggy]

If I remember correctly that was mostly so they could recap a whole conversation that already happened without actually recapping it. After many of those silent scenes the other characters would be filled in on all the details we were already appraised of.

[Alberel]

If I remember correctly that was mostly so they could recap a whole conversation that already happened without actually recapping it. After many of those silent scenes the other characters would be filled in on all the details we were already appraised of.

Pretty much this. Whenever your character silently mouths things during conversations they are relaying information that we have already been given. It helps avoid massively repetitive dialogue and allows us to give our character the voice and personality we want rather than being forced to choose from a selection of options that would never suit everyone.