Lord of the Rings: The Two Towers - Dude, Where's My Horse?
Several times, Aragorn's horse, Brego is in the movie. However, if you look, sometimes his horse is different! Sometimes, it is light brown. other times, it is almost black, and has a white diamond on his head!
I commend you for noticing this, but as king Aragorn would have different horses to choose from to ride. Additionally, in the extra documentary type things on the DVD they explain that they had to use many different horses, because of different behavioral problems, although I don't know of any problem with Brego that would have prevented them from using him throughout the movie.
Speaking of slipups having to do with horses - in the TT EE, Aragorn sees Brego in the stables in Rohan. I think he's dark brown with a white star like the poster said. Aragorn says to let him go because he's seen enough of war.
Later on, after Aragorn has been dragged off the cliff by the orc, Brego shows up and takes him back to Rohan. When he finds Aragorn, he had to have been set loose, otherwise why would he be there. BUT - he still is wearing the bridle. Why would they have left the bridle on him?
Let me see if I can clear this up. Aragorn does have two different horses! But you have to have the Extended Edition or else it's not very clear. When Aragorn, Legolas, and Gimli are tracking Merry and Pippin, they meet Eomer and his men. After they finish talking, Eomer gives them two horses - a white one and a LIGHT BROWN one. Aragorn rides this horse for a while. When they get to Edoras, Aragorn calms down another horse and Eowyn says, 'His name is BREGO.' Brego is dark brown with a white star! Aragorn still rides his light brown horse until he falls off the cliff in the battle with the Wargs. Brego finds him by the river and from that point on (end of TT through ROTK) whenever Aragorn is riding a horse the horse is Brego. Hope I helped!