One of the top egg producers in the U.S. confirmed that a farm tested positive for cases of bird flu over the weekend, the company said in a statement Tuesday.

The humble egg, one of nature’s perfect foods, a self-packaged, relatively inexpensive source of protein that can serve as a lowly hangover remedy or help a souffle rise to heavenly heights, is also a great teacher. It’s helping Americans understand how a free-market economy works: When demand is high and supply is low, prices rise.

The Department of Agriculture warned egg prices may increase more than 20% this year, after December saw a year-over-year increase of 36.8%.