As for
the Ring "accidentally falling" on (or off), one cannot fault Mr. Jackson for that particular trait. We are told by the author that the Ring does just that.
Frankly, one of the most unbelievable things that
Tolkien wrote was the part in which
Bilbo with
Sting in his right hand, fleeing for his life from
Gollum up the
orc tunnel, PUTS HIS OTHER HAND IN HIS POCKET just in time for the Ring to "accidentally" slide on to his finger! Considering that NO ONE who is running EVER puts his hands in his pockets, this required almost as much suspension of belief as
Arwen sneaking about in the dark at
Weathertop. However, it is lated explained by the fact that the Ring influenced the
Hobbit to do this so that it could make him invisible and save his life - this allowing it to escape from Gollum.
However, if that is the case, then we must expect that the Ring is equally capable of doing the same thing at other times. In
Bree, <itb> it "slips" onto
Frodo's finger while he's dancing around on a table in an attempt to draw attention away from
Pippin who is just about to "spill the beans" about Bilbo's disappearance at his party. Now, why he had his hand in his pocket on this occasion is a little plot stretch, but again, he felt "uncomfortable" and the Ring must have influenced him so that it could betray its presence to interested parties in the room.
In Mr. Jackson's case, he could hardly make the audience understand what happened if the Ring "slipped" on Frodo's hand while it was in his pocket (we would not have been able to see the action), so he did the scene in the only way open to him. However, it is no more unbelievable for the Ring to "fall" onto Frodo's hand as it did in the film, than it would be for it to "slip" onto his hand as it did in the book.
In this case, I think, the Director cannot be faulted for his handling of the incident.
