Deliberate mistake: When the two Confederate and Union soldiers meet across the river and trade coffee/tobacco, you can see the other side of the bank behind them. It looks at least 50 feet away, yet before they were able to talk to each other without shouting. Also, the Union soldier raises the pipe to his mouth in his right hand, which switches to his left in the next shot. There is also a mist present at the beginning and end of the meeting, but not in the middle. (00:37:55)
Deliberate mistake: In the final race of the film, Seabiscuit performs a flying lead change at the gallop while crossing the finish line, in the famous shot taken underneath his neck. Horses normally only switch their leads around turns while racing; it's something done to relieve pressure on the leading foot. From taking the shot over and over again, the horse playing Seabiscuit was probably tired out and a little tender and began to perform lead changes in other places in an attempt to be more comfortable.