Deliberate mistake: There is no way Ichi's blade could have cut the one man vertically in half, as shown in the movie. The blade is only a couple of inches long, not nearly enough to slice through the man. When we see the blade shooting through the back of him, it is obviously a different, longer blade.
Deliberate mistake: When Suzuki has the boiling oil poured over his body, his skin doesn't react quite realistic. You only see it scar up a little bit, when realistically, the heat would be melting the skin right off.