I think Reindeer have been known to also seek out fly agaric. I have not personally seen them do this so I cannot say. Dolphins and reindeer "getting high" is hearsay until I see it for myself
Same component as catnip I would wager.
What is interesting is that all the things that are sought out by animals don't have the same effects on us (such as catnip).
In nature these occurrences are quite rare.
Drunken animals is much more common but I don't think they did it on purpose.