Tentacles literalizes the fear of falling in love with someone who turns out to not be the person you thought they were, and losing your own sense of self in the process.
In an interview with Black Girl Nerds, screenwriter Alexandra Pechman said that the inspiration for Tentacles came from romantic relationships. “I think it’s a pretty universal experience that you worry that you’re falling in love really fast, and moving in together, and all of the different things that come with relationships, and then you’re sort of wondering, ‘Where did I go?'” she said. “And that’s something of what these characters start to experience, but in a horror lens.”
Everyone has been in or watched a loved one go through a relationship like Sam and Tara’s, where the feelings are so intense that red flags get ignored and the relationship becomes their entire life, to the extent that relationships with friends and family atrophy and mental, emotional, and even physical health get neglected. By the end of Tentacles, all of those things become literally fatal for Sam. The demon needed to latch on to someone in order to have an identity, and it happened to be him. There were others before him, and there will be others after him.