Migi will reunite with Shinichi in the end
- This is from episode 22 where Migi appears to have died. The parasite that calls using Shinichi's voice is separate from the one that attacked and failed to kill Gotou. It also had significantly more mass than the one that got killed by Gotou. Therefore, the remaining part of Migi will survive by latching onto Gotou's body and find Shinichi again by this method.
- this appears to be true by the next episode.
The parasites actually have a full range of human emotions
- The parasites have only appeared recently. Even the oldest ones are not much more than a month old. It is likely they only develop their full range of emotions, such as empathy, after they grow older and have more time to self reflect. They are like infants with full human intelligence who are driven by the impulse to eat humans and die too soon. Both Migi, who didn't consume a head, and Tamura Reiko were more curious about humanity and themselves and always tried to understand how the world worked. This caused them to develop faster than the others.
The Parasites are decommissioned bioweapons from a distant planet.
- No earthly organism behaves the way they do, or does the things they can through Shapeshifting. One possibility is that they were created by, a race on a planet in a distant galaxy. Created for the purpose of eliminating their enemies on, yet another planet by infiltrating their ranks and taking over, the bodies of certain individuals and destroying them from within. But they were too unpredictable and thus decommissioned, and then disposed of with the last remaining eggs being cast into space. There they drifted in stasis until one day, they ended up on Earth.
Kana's unique sense is because she's a parasite.
- We already know from Migi and Jaw that the process of taking over a host can fail, it's possible that she had one that screwed up the process even more than them or had a defect that caused the process to fail. It could even be in some sort of comatose state somewhere inside her which would explain why she was never aware of it and only experienced this one alteration to her abilities, which is notably one of the most prominent traits displayed by parasites on countless occasions. It's certainly a much more elegant and reasonable explanation than introducing some supernatural element to a setting that is otherwise surprisingly grounded.]] Uragami on the other hand was probably just a lunatic with far too much intimate experience with the human body. He's completely incapable of telling if a parasite is standing right next to him until he looks them in the eyes, so mundane observation explains it without any need for alien senses.