Visible crew/equipment: When the now zombified "Speedball" approaches the cell bars to ask Herbert West if he has any other drugs, you can see a black wire/cord holding him up. (01:24:15)
Revealing mistake: When Rolfe is walking down the hallway to Sally's apartment, there is an orb where the hallway is lighter colored and his legs seem to jump and undulate due to the special effect used to hide the fact that the actor is actually full-sized, walking on his knees.