Actually lengthening your tongue is not possible. The tongue is a muscle and has a set amount of muscle fibers or muscle cells. Some people have a surgery to remove the skin under the tongue that allows for more movement and gives the appearance of a longer tongue.
1 Additional Answer
There is really no way you can lengthen your tongue on your own. The only real way you can add a small amount of length to your tongue is to have it done surgically. You can have the frenulum under your tongue cut allowing your tongue to come out farther.
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