Traits

The Tailmouth is an extra grown layer of skin over its tail resulting in a faux head where the true tail resembles a writhing tongue.  A weak muscle keeps the mouth closed most of the time, though it can be manually popped open by tugging at the zipper-like feeler located on one end of the faux mouth. 

This trait is primarily used for intimidation and occurs more often in the wild, the faux mouth snapping open when the leech is frightened or enraged.  Oftentimes when people report sightings of a two headed leech, careful examination must be conducted to make sure it wasn't simply a startled leech with a Tailmouth hood. 

Note: This is not a second head, and should not be treated as such. Traits that can appear normally over the rest of the body/tail can be applied here, such as see-all eyes and spikes. The overall shape should stay basic tail-like.
This can be applied successfully to any tail trait, but both Tailmouth and tail trait must be visibly obvious.