2 year old Selective Hearing Syndrome and other nuggets of wisdom

I have began to wonder why none, not one,of the parenting books mentions that around the age of 2 children develop selective hearing.Hearing only the things that they want to hear and specifically those things that you don't want them to hear such as the occasional stump your toe curse word or the fact that your friend needs to lose a couple pounds. Of course they choose to hold on to these nuggets until the most inappropriate times for instance, said friend's nervous breakdown over her looks, or they blurt out some unexpected four lettered gem in the middle of mass.Why is this information not labeled with a warning in the parenting books. Is it just another one of those secrets we keep because it is too much fun to watch the provisionals experience the embarrassment and humiliation that we ourselves did, not so long ago?Beware this is quite frequently co morbid with Constant Repeat disorder. In a nutshell, not unlike my child, your child ignores you and repeats anything they say constantly as to make sure that you have not acquired their selective hearing syndrome.My daughter's favorite repeat phrase is " M..o..m...m.y...EAT!" It is usually repeated in sets of no less then 7 times. Furthermore, even more concerning then the 2 year old selective hearing syndrome, there is the very common but temporary ( I am hoping) 4 year old complete deafness disease. This is a little more frustrating because the onset is normally around the age of 3 to 3 and 1/2 years of age and continues on to about the age of 6, only to reappear at around age 11.So, that is something to look forward to in the coming years. My daughter's particular strain of the disease leaves her completely deaf to any and all requests from her father and I, of any kind, especially those requests that pertain to the well being of her little sister, aforementioned victim of selective hearing syndrome. Sometimes it can be quite scary when you are asking, repeatedly, for the child to stop beating on their sibling, sitting on their sibling,annoying their sibling, doing something dangerous, to eat, be quiet or clean or pick up anything and the child simply does not hear your voice in any form. They become completely oblivious to the parent who is making said requests. Sometimes, we are overcome with the desire to shake said child but don't give in. At the very moment you move towards the child, like a bunny, they scamper and scurry to another room. Leaving you even more frustrated because with 4 year old complete deafness disease, once in another room deafness is absolute and there is no hope for said child to hear anything you will ever say fro the remainder of the day..possibly ever again!