There may be no more-radioactive term in the English language than what we now almost always refer to as the 'n-word' - itself a coy means of linguistic sidestepping that is a sign of how perilous it is to utter the thing in full, even in conversations about language.

Credit or debit cards, for starters, are nothing short of shoppers' Novocain. Even in the age of digital purchases and virtual money, we still attach a special value to dirty paper with pictures of presidents on it. Handing some of that to a cashier simply hurts more than handing over a little sliver of plastic.

It's one of the worst-kept secrets of family life that all parents have a preferred son or daughter, and the rules for acknowledging it are the same everywhere: The favored kids recognize their status and keep quiet about it - the better to preserve the good thing they've got going and to keep their siblings off their back.

Kids whose puberty begins too soon face not just psychological risks, but physical ones too, with an increased likelihood of cancer, as well as skeletal changes that could prevent them from attaining their full adult height.

If you're an older sibling and you have a younger sibling who needs mentoring or is afraid of the dark, you develop nurturing and empathic skills that you wouldn't otherwise have.

The brain sits snugly inside the skull, but it's not a completely flush fit - there is still a layer of fluid between bone and soft tissue that serves as a natural shock absorber. Some shocks, however, can't be absorbed, and when the head gets clobbered too hard, the brain can twist or torque or rattle around inside its skeletal casing.

As the National Football League and other pro sports increasingly reckon with the early dementia, mental health issues, suicides and even criminal behavior of former players, the risk of what's known as chronic traumatic encephalopathy (CTE), is becoming clear.