No one has actually seen it, but a fairy interpreter asked a fairy and they described it as just a cloud of smoke and once in a while you trip over something in the floor.  The fairies purposely leave their trash in the floor because they think it is funny when people trip over them.
Inside the fairies church, Inside Church
cricket
bluebird
I am a bluebird that has made a nest in the castle walls. The king loves to listen to me sing every morning. My song fills the castle with music every day.
Oh I would never hurt a creature as nice as you! Thank you! I no that I am small and most birds would try to catch and eat me. I'm no monster! Where do you come from mr.cricket? From the fields outside the fairies church. I try to stay there mostly, because the fairies are always playing tricks on people in here These faires are real jerks, they really like to make a mess and they think its sooo funny. It's all fun and games until someone gets hurt.... and that is not funny! Here take this, maybe it will help with something. it seems to come wherever I go! What can I do with this shiny glitter?  Maybe make a wish! The fairies always want it from me! That is true! I have seen a couple of them with the glitter, sprinkling it all over everything that they come in contact with What do you think that smoke over there is coming from? It is what the fairies call the church! Another fairy told me that!