Continuity mistake: When the surgeon dies, Francis grabs Logan's arm but a shot later he is grabbing his chest.
Continuity mistake: The cut on the surgeon's shirt is suddenly reversed a shot later.
Continuity mistake: When the surgeon's face is cut he turns his head to the right. A shot later he faces the left side.
Revealing mistake: At the surgeon, the laser cuts the stretcher (a superimposed red light), but when the lasers go berserk they don't cut anything, revealing they're just lights.
Continuity mistake: When Logan empties his pocket in the scanner, they keep changing positions between shots. (00:21:30)
Continuity mistake: Francis walks towards an identity detector machine where he drops stuffs inside and places his hand. The stuff disappears and reappears between shots.
Continuity mistake: Logan and Francis meet a bleeding man by the steps and Logan walks ahead. A shot later he is next to Francis.
Revealing mistake: When the film starts Logan and Francis chase a runner who stands by a column, the squibs used to allow for the sparks and FX are visible.
Continuity mistake: When Logan talks to Francis about his baby, Logan's hand swaps between being by his side to being on the glass. (00:03:08)
Revealing mistake: In the opening scene at the nursery, a flesh colored clip is visible on the baby's hand. It is holding the white crystal to the center of his palm. (00:02:48)
Visible crew/equipment: Right after the Carousel segment, a red-clad man is running because his life-gauge says he's 30. He runs through a semi-open corridor that has dark tan bricks. A moment after he passes through the area, and turns back to see Logan aiming at him you can see a spark emitting device has been colored the same as the bricks, but noticeable. It is a special effect to complete the scene.
Answer: In popular American lore, the Sandman is responsible for putting sand over your eyes to make you go to sleep. In this context the "sleep" is a euphemism for death, and the enforcers are responsible for making sure that everyone dies on time.
Phoenix