This episode is similar in name to an episode of Dark Angel (2000) in which Jensen Ackles also was a recurring character. Also the name of Dean's "son" in this episode is the name of the character Jensen Ackles played in season 1 of Dark Angel.
The reflections of the changelings in this story appear to be heavily inspired by a creature from a Star Trek (original series) episode called "The Man Trap" (season 1, episode 1). The big difference, the creature in Star Trek fed on salt whereas the changelings in this episode fed on other bodily fluids.
Sam states that changelings feed on synovial fluid from the mothers and that they always feed on the back of the neck. Synovial fluid is a type of fluid found only in the spaces between joints, it acts as a form of shock absorption it helps lubricate and also helps remove waste from the joint space. All humans have synovial fluid, not just women, and there is very little in the cervical vertebra. The majority of synovial fluid is found in larger joints such as the elbows and knees, so there might be other reasons as to why these creatures only feed on the mothers and only on the back of the neck.
"The Cicero Pines Motel" location has been used many times throughout the shows seasons. Used is S1 E17, S2 E3 as well as S12 E8. It has had many different names in different episodes & a major remodel on the exterior for its appearance in season 12. The giveaway is the the "pyramid" shapes over the front doors or the wooden beams protruding from overhead. Those were covered though in the remodel.