You searched for:
It's gotten to the point where Thor just assumes most animals are secretly his brother.
He's very protective of his brother. He tends to act before he thinks. These don't always make for a great combination.
Or: Five times Thor was mistaken in thinking a random animal is Loki, and one time he was right.
So here's my first multi chapter story. It's set after infinity war an Thor, Loki, Valkyrie and even Bruce are enjoying life in Norway on New Asgard, (Very thoughtfully named Asgardia) After returning from a trip with the Guardians, Thor falls ill, from what no one can tell but as the virus grows stronger, Thor grows weaker and Loki works against the clock to figure out what happened whilst Thor was away and what is wrong with his brother.
Things Tony Stark wanted that evening: a movie to watch, junk food, and beer.
Things he got instead: two unexpected guests from outer space and some very, very bad news.
Life is good in New Asgard. The Asgardian refugees are thriving and the Odinsons are great leaders. It seems like nothing can go wrong.
Then, Thor goes missing during a diplomatic trip to Vanaheim. Loki is worried sick about his brother, who seems to have just vanished into thin air. Just when things seem hopeless, Thor returns. He has no memory of going missing or where he was. Loki realizes something is terribly wrong with his brother but without Thor's memories, he doesn't know where to begin searching for answers.
Death is not absolute. Not if Thor Odinson has anything to say about it.
Thor and Heimdall agreed that they'd both watched Loki die too many times. Because of that, it was understood that if it was within their power, neither of them would let it happen again.
With that in mind, Heimdall sends Loki to earth along with Bruce.