In this shot Luke’s saber goes through the railing here without damaging it.
http://www.youtube.com/watch?v=pVWGmQgHDZc&t=2m17s
The engines of a Y-wing that passes here in this shot are not light up
https://www.youtube.com/watch?v=zG2PL3bUH1s&t=1m04s
When the shield generator explodes, a piece of shrapnel flies towards the left side of the screen and then bounces back off from the inside of the wall it was housed in.
https://www.youtube.com/watch?v=BN3kISlsSCQ&t=0m09s
