Continuity mistake: In part 3 an agent of the Red Skull tweaks a letter on a statue to activate the third and final "Sleeper." At a distance you see the statue depicts someone on horseback, one of the horse's hooves is above the ground. As the agent tweaks the letter, all four hooves are on the ground.
Continuity mistake: Part 3: As you see the third "Sleeper" (a giant bomb shaped like the Red Skull's head) note the position of the monocle. First it's on its right side, then its left side, and back again to its left side.