I can see where you're coming from, but I'm afraid I still interpret that to mean he had used his illusions to take the form of a snake, and less that Thor literally meant transform. Partially because it feels that real transformation, even if just as a snake, would have been something shown in the movies that featured Loki, at least once. Just my personal interpretation, sorry if it's a tad disappointing.Nah, Thor explicitly said "He transformed himself into a Snake" and "he changed back"