Right at the start, when Zack is hanging on the tree branch, the long sneaker laces are in front of Cody's shoulder, but when Zack falls, they're gone, though the sneakers have not moved.
While everybody is standing in front of the Liberty Tree to protect it, the real Liberty Tree felled in 1775 by Loyalists. All that is left is a plaque commemorating it.
In the part with Zack's dream you can see Brenda's natural hair under London's wig.