George wrote:

I'm referring to simulated launch conditions, of course. One
thing I noticed from the ET video is that it appeared that the
ET shell was flexing quite a bit. Did anyone else notice this?

You evidently saw the normal twang caused by the side-mounted main
engines. After an extensive standdown such as this one, it's been SOP
for KSC to conduct a Flight Readiness Firing (FRF) prior to launch.
This flexes the tank in advance, to a large extent.

Speaking of the (non-FRF) approach taken this time, after the launch
Griffen told the media that we owe "this team" a "large debt of
appreciation" for its "sheer gall." Bill Readdy, Griffen's deputy,
immediately chimed in with "Amen!"

I think the sheer gall belongs to Readdy, Griffen, and Bush. However, I
wouldn't want to influence anyone who hasn't the time to look further
than the media reporting by the likes of Bill Harwood and Jay Barbree
at the Cape.

Challenger's Ghost