If Hermione’s testimony had changed from last time, I’d have guessed that McGonagall was mouthing a spell or trying to Confound Hermione so she gave a different testimony under Veritaserum.
Since that isn’t the case, she was either trying to:
a) provide moral support for Hermione (“Keep strong” and such)
b) communicating something. If it’s this, then I strongly suspect that McGonagall is cooperating with future Harry in some rescue plan. She might be communicating a simple message like “Don’t worry” or “We’ll get you out” which would imply that she has some extra knowledge about how things are going to play out.
But what she told Hermione shouldn’t be very important as there was no way to know that Hermione, in her tired state, would understand the significance of whatever McGonagall mouthed.
If Hermione’s testimony had changed from last time, I’d have guessed that McGonagall was mouthing a spell or trying to Confound Hermione so she gave a different testimony under Veritaserum.
Since that isn’t the case, she was either trying to: a) provide moral support for Hermione (“Keep strong” and such)
b) communicating something. If it’s this, then I strongly suspect that McGonagall is cooperating with future Harry in some rescue plan. She might be communicating a simple message like “Don’t worry” or “We’ll get you out” which would imply that she has some extra knowledge about how things are going to play out.
But what she told Hermione shouldn’t be very important as there was no way to know that Hermione, in her tired state, would understand the significance of whatever McGonagall mouthed.