TMBTM said:

Just a very little thing I never saw though. It's also on the original footage. It's at 1:35: Don't we see something that looks like a laser hit appearing on the back of the AT-AT, but without any actual laser beam hitting that point?

Yeah, it definitely looks like Luke was supposed to hit those points. This kind of effect is also clearly evident at 1:45. Note the main body area just above the AT-AT's front legs and you'll see two blaster hit the armor and leave two marks.

I guess the Snowspeeder's blasters would have to angle themselves in order to hit those marks which wouldn't be all that realistic given how mounted they look.