Why does my 4 nth old baby keep eating her fingers?

At that age, baby is discovering how her fingers and feet work and it is likely that that her fingers are pretty much her new favourite things. Putting them in her mouth is part of exploring them and acknowledging that they are part of her and that she has total control over them. Now that this milestone has happened, be careful to ensure that baby does not accidentally put other items in her mouth that might be detrimental to her. Keep an eye on the curious little one!