During Marshall's training with the Strength slapmaster, his right hand glows golden. But when he slaps the Accuracy slapmaster, he slaps with his left hand.
The angle of Marshall's hand in the slow motion sequence changes from the side view to close up.
The Calligrapher (whose training is all about accuracy and being thorough) states that Garfield was only president for "like, 4 months" before he was assassinated. "Like, 4 months" is not only implying an approximation, it is inaccurate. Garfield was president for 6 and a half months and he died, not from the attempted assassination as is commonly thought, but from doctors probing into the wound with unsterilized fingers and instruments.