My mom used to get so upset when we used to let our kids lick things, but we just sort of thought; you know, I know what cement tastes like, and carpet, and rubber, etc. I haven't put any of that stuff near my mouth recently, so that memory is coming from somewhere....... I think kids are building a sense memory when they lick things.

*disclaimer* we obviously didn't let them lick dangerous or poisonous things.