The "Alien" constantly switches between human-sized (practical) and around the size of an elephant (CG).
In many scenes, such as the fights between Valentine and the hunter, in one shot the hunter is turning invisible, and in another it is still fully visible.
When all the characters are having their first meeting, the clock doesn't have batteries in it and doesn't change.
Laser effects frequently mismatch with sound effects.
When the hunter is shooting at Valentine who is behind the car, laser sound effects come too early for his bullets.