Moose is an animal that is often referred to as unintelligent. This has also been used to describe a person who is not acting intelligently. I guess the loose is a compliment.
I love the fact that the words were used together and maybe it would mean something together too, but it doesn't. They are best looked separately as loose is the usual word that describes something bring slack, and the moose as the unintelligent being. Reading it backwards, it does not make much meaning but i guess that is how new words are found.
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