When Cathy meets Heathcliff for the first time on the moor (about six or seven minutes into the episode), Heathcliff has a lock of his hair over his forehead, and it disappears suddenly, then reappears and disappears again.
A few minutes in, the first shot approaching young Cathy from the back reveals her dress has a modern zipper. The story is set in late 1800s England; though the zipper was technically invented in 1893 in America, it was not met with enthusiasm. It was finally patented in 1917 and first used in clothing in 1925.