When Spock first falls ill, he's on the bridge. Previous shots show the usual bridge crew on the scene, but as Kirk calls Sickbay, Dr. McCoy stands to the right of Kirk's chair already, negating the need for the call, but in the next shot (a close-up of Kirk), McCoy is gone again.
When Spock enters Sickbay, he is heard first knocking on the door. The doors are automated to open when someone comes near, so knocking on them would open them. Star Trek has always had a push button outside the doors to activate a notification tone, letting people know someone is outside.
The opening shot of the bridge shows the usual allotment of crew on the scene, with every seat filled, but when the perspective changes to a close-up of Spock, the red-shirted crewman seated near the turbolift doors (later named as Scott) suddenly goes missing. Later on at 9:19 the same holds true: a shot of the bridge with every seat filled followed by a close-up of Spock with an empty chair behind him.
At 10:04, Lt. Arex takes over at Spock's station. The chair in the background is empty where there should be a red-shirted crewman seated (later indicated as Commander Scott). The scene repeats at 11:58 and 12:07 and 19:34.
A close-up of Sulu at 14:21 shows another empty chair in the background. All seats should be filled during the time of emergency that they're in.
The Orions' first attack on the Enterprise comes from the starboard (right) side, but Kirk orders hard to port (left) in order to face them head-on.
The final scene takes place in Sickbay, but one shot at 22:05 shows the bridge in the background.
When McCoy hails the bridge and talks with Kirk, who is seated in his command chair, the angle changes, and McCoy has been inexplicably drawn in standing right next to the command chair. No one acknowledges his presence, and in the next angle change, he's gone again.
Nurse Chapel and the Huron lieutenant are both voiced by Majel Barrett and both drawn the same (with blonde hair) making them erroneously seem like they're identical twins.
McCoy says something through the intercom from Sickbay, but he is standing next to Kirk on the bridge.
At 13:03, Lt. Arex is shown back at helm controls, but a moment later he's manning Spock's station again. Neither position should go unmanned and it's surprising that an extra crewman hasn't been summoned to the bridge by this time.
After Kirk, Scott and Uhura board the "Huron," only Captain O'Shea is mentioned as recovering in sickbay. His other two crew members are seemingly forgotten.
Everyone pronounces the Orion Pirates as OH-ree-an pirates instead of oh-RYE-an Pirates, as they are called in all other Star Trek productions involving this group. These include Yesteryear (1973) in which Kirk mentions exploring Orion's past.