Bridges flex for the same reason as planes, and to a greater degree. Bridge flex has little to nothing to do with structurally deficient bridges (which is certainly a serious problem). Brand new bridges have plenty of flex, by design.

I had one on a recent flight; sadly my phone was dead or I would have taken a bunch of pictures. I'd guess about 90% of my flights I sit in an aisle seat, so I don't often have a chance to look out the windows.

I only get concerned when one wing falls off and another passenger
notices and asks "can we fly on one wing?"

Scratches on the wings are pretty much identically equivalent to dings and rock chips on the front of a car. Just as I'd never worry about getting into a taxi cab because the paint on the front was a little chipped, I also never worry about similar cosmetic damage on aircraft...

when I sit by the wing, especially if it is raining, I end up thinking of the the twilight zone episode with William Shatner. :eek:

I only worry if seated next to this guy

http://www.defordmusic.com/wp-conten...changes-do.jpg

(One of my all-time favorite Far Side cartoons...)

Flew on the BA 787 from AUS to LHR a few months back and was sitting just behind the wing so I had a good view of the wing through the window. It is kinda scary to see how much those wings bend, but cool at the same time. Other planes I don't see wings bend all that much, but on a 787 it was definitely noticeable.