I did not know that yesterday!

Unlike my sorry collection of beer cans, Stradivarius violins have a lot more than just sentimental value. In fact, one was recently auctioned for $3.5 million. Such a large sum begs the question -- what makes Stradivarius violins so special? As far as we can tell, there are three main reasons.

One, they're rare. If our time in Economics 101 taught us anything, it's that often, the rarer something is, the more valuable it becomes. According to several sources, there are less than 700 Stradivarius violins in existence today (considerably less than the number of beer cans even in Wallis and Futuna!!).

Two, they're old. Each violin was constructed by Antonio Stradivari, whose work was commissioned by both England's King James II and King Charles III of Spain. Stradivari, who unlike many great artists, was actually appreciated in his lifetime, died in 1737. Going with him was his method of construction.

Which brings us to three: A Stradivarius violin sounds much better than anything else. Some say the glue Stradivari used is responsible. Others believe it's the density of the wood. In 2001, a biochemist named Joseph Nagyvary attempted to "emulate" the sound. He concluded the chemical borax is the secret ingredient. According to Nagyvary, borax not only protected the wood, it also "bound the molecules of wood together, altering the sound."

Nagyvary sells "authentic recreations" with a focus on tone and material. They're not cheap, but we're guessing you can pick one up for less than $3.5 million.