These things know Basic?
I won't tell you when, but there is an Ewok who clearly says "He's a wise one" in plain English!

Maybe a ventriloquist?
Ok, picture this: the Rebel Fleet realizes they have fallen into the Emperor's trap. The situation is very tense on Admiral Ackbar's Cruiser, the Home One, and his crew is working frantically to keep the situation barely under control. There is a small problem though, they can't move their lips! Yes, check out the other Mon Calamaries in the background, right behind Ackbar, when they talk, they don't move their lips!

Scouting Scout: The Drunken Trooper Legend.
This blooper actually has a story behind it. According to unknown sources, an actor playing a Scout Trooper on the Ewok Battle on Endor went out to a night in the town with his trooper armor still on. He got so drunk that the next morning, when he woke up, he was lying on the street, still with his armor, but his helmet had been lost. He got back to the filming location and just stood there on the scene. Nobody noticed a drunken trooper standing amongst the other troopers without his helmet, and the drunken trooper made it into the final cut of the film. Check him out, he looks very funny!

A New Hope ~ Empire Strikes Back