Cass can't just read lips all the time because unless she's paying very close attention there's a high margin for error, and especially as soldiers in combat situations it could be difficult to have constant sightlines on everyone's mouths at close enough distance to read, especially if multiple people are in conversation and attention needs to be constantly redirected.
Dominic D
2020-07-09 13:15:16 +0000 UTC
The Doctor's death at Lake Silencio had some bootstrap aspects to it with the younger Doctor receiving an invitation that he would later send to himself.