so i have just recently realized that my tongue has this wierd thing on it. idk how to explain it other than it looks like a thin gray covering towards the middle and back on my tongue. i have tried brushing my tongue and using substances like Listerine to try and get rid of it. i am not sure what it is.....should i be worried? it tends to go away when i eat because i guess the food scrapes it off but it comes back. i was wondering if anyone could tell me what it is, and what i should do about it? i dont think it is a STD but i want to know what is happening on my tongue. if anyone can answer, you response is much appreciated.