At the beginning of the show, Kirk picks up a bunch of "flowers" (actually some scrub brush) for McCoy to give to Nancy. Kirk then throws them on the ground. The camera pulls back, and the "flowers" are nowhere to be seen. They should be lying on the ground.
When Kirk walks into the turbolift, returning from his mission to the surface of M113, the cameraman's shadow can be seen following him in. And, this shot is used in many additional episodes of the show.
The "vampire" has lived without salt for a year, yet once prey shows up, it seems to desperately need salt every few minutes. However, it could be stocking up on salt supplies within its body just as a camel stocks up on water, or as humans and many animals store calcium and other rarer minerals into bone tissue.
Dr. Crater wants to keep the creature alive. Since Starfleet/The UFP is in the business of discovering and preserving endangered species, why didn't Crater, upon beginning his understanding with the creature, simply get in touch with them and order a lifetime supply of salt? There is absolutely no reason to resort to murder for something that would be willingly granted legally.