Does she? I never really paid that much attention to it when my girls did it, but I know DS2 doesn't do anything like that. If she does, it's not something to be concerned about really - OK so it wouldn't be OK at the dinner table LOL, but she too little to understand what was going on if you got her to stop. Are you worried that it might make her grow up too quickly and become sexualised too early if she gets old and decides that she wants to do it because it feels nice? It would be really intersting to read the article if you could copy and paste it though.