Well, Whadya Know

Why do we call a test for authenticity or usefulness the
"acid test?"

The origins of this phrase were quite literal. More than a century ago, when much
of the population lived in rural areas, the itinerant peddler
was an important person. Not only did he sell all sorts of
manufactured goods otherwise unavailable, he also bought old
objects made of gold. For this purpose he needed an easy way
to estimate the gold content of, say, an old spoon. He did it
by nicking it slightly and pouring nitric acid on the
indentation. The color the liquid turned revealed the
percentage of gold present.

[source: Why You Say It by Webb Garrison]

When do bears emerge from hibernation?

Some trivia books still try to pose this as a trick question, stating that bears don't emerge because they never hibernated in the first place. The bear's body temperature doesn't fall as much as that of other hibernating animals, and this was once thought to disqualify them as true hibernators. But now we know that their higher body temperature is simply a function of their larger size.

Like other hibernators, bears don't sleep through the winter, but rather wake up periodically and eat what they've stored in their cave. They emerge for good when average temperatures are above freezing.

[source: The World Book Encyclopedia]