Final answer:
The animal in question is a flatworm, or trematode, which is a parasitic organism that lives initially in a robin, and later makes its home in an aquatic snail, causing noticeable physical changes to the snail.
Step-by-step explanation:
The animal described in the question is a parasite that lives inside a robin and then transfers to an aquatic snail, eventually migrating to the snail's tentacle, causing it to swell and turn bright blue. This animal is a flatworm, specifically a type of fluke or trematode, which are known for such complex life cycles involving multiple hosts. The behavioral manipulation of the snail is a part of the fluke's life cycle, intended to make the snail's tentacle more visible to predators such as birds, which are the next host in the parasite's life cycle. Once ingested by a bird, the fluke can continue its development and reproduction.