Stand-up comedians have long joked that some things, like the actual components of chicken nuggets, are better left mysterious.

Recently, Mississippi researchers found out why: two nuggets they examined consisted of 50 percent or less chicken muscle tissue, the breast or thigh meat that comes to mind when a customer thinks of "chicken."

The nuggets came from two national fast food chains in Jackson. The three researchers selected one nugget from each box, preserved, dissected and stained the nuggets, then looked at them under a microscope.

The first nugget was about half muscle, with the rest a mix of fat, blood vessels and nerves. Close inspection revealed cells that line the skin and internal organs of the bird, the authors write in the American Journal of Medicine.

The second nugget was only 40 percent muscle, and the remainder was fat, cartilage and pieces of bone.