Sticking it out

Awhile back, Piper discovered her tongue. Since then, she has been a little obsessed with it.  It is ALWAYS sticking out.  Sometimes it seems like she is concentrating on something, and then sometimes I think she just likes sticking it out.  What is this all about?  Does anyone know?  It is pretty cute. But also perplexing.  And the paranoid mom side of me wants to know if there is something wrong with her mouth ...