Your tongue can actually tell a lot about your health, search tongue diagnosis TCM
Traditional Chinese Medicine,
I suggest you visit a Chinese acupuncturist, and have them look at it, they can tell you the exact cause, and what its indicating.
Check this link below for more information.
http://www.sacredlotus.com/diagnosis/tongue/index.cfm
Look on another website
A black line down the center of the tongue can indicate various conditions, including poor oral hygiene, a buildup of bacteria, or a reaction to certain medications. It may also be associated with a condition called lingua villosa, where the papillae on the tongue become elongated and discolored. In some cases, it could signify an underlying health issue, so it's advisable to consult a healthcare professional for a proper diagnosis and treatment if it persists.
The line of your tongue is there because when the body is forming it is split into sections. The line shows where the face sections came together.
what is center line plan construction
It means to kiss
A deep line in the center of the tongue, often referred to as a median groove, can indicate various conditions, including dehydration, nutritional deficiencies, or certain diseases. It may also be a normal anatomical variation in some individuals. If accompanied by other symptoms, it may warrant a consultation with a healthcare professional for further evaluation.
If you stick your tongue out, you poke it out of your mouth.
It's slang for going down on a girl aka tongue action.
No passing.
divided highway
It means that your lane cannot pass.
Its called ankkbee it sorta mean F you only kids do that though in japan
No passing when driving in that direction while it is solid.