Liar Liar pants on Fire

So it has happened.  Roxy has started telling lies.  Oh it used to be little cute things like when we were mad at her or sending her to timeout she would say "ouchie" so that we would kiss her and not be mad anymore.   But now she is taking it a step further.  We are trying to get in the habit of sitting as a family for dinner and eating together.  Well yesterday she was done and wanted to get down, but she had not eaten anything and Rich and I were not done so we told her no.  She starts crying and saying "done, done, done"  and making the sign language sign for finished.  We don't let her down and then she says "poop" to get us to get her down and go change her.  She was not poopy she just wanted down.  Shysty charachter.   How do they know to manipulate and tell fibs this earlier.  Is it innate or when I say the backyard is broken because I think it is too hot to go, does she understand that mommy is lying.  What do you think?