These are a popular delicacy in China, supposed to enhance male prowess, and improve skin tone for women. They seldom appear in North American cuisines. In China they are available in both pink and black, but the black fleshed silkie chickens are still a very small specialty item in North America, so the black balls are not available here.
Rooster testicles are larger than you might think, but they need to be. A rooster is expected to be up at the crack of dawn, crow his heart out - then "service" 20 or more hens during the day. No slouch he - your rooster is a busy bird. The photo specimens varied greatly in size from 1.13 inches long, 0.6 inch diameter and 0.13 ounce to 2.4 inches long, 1.13 inches diameter and 3.13 ounces. Our ever faithful red kidney bean is in the upper left corner for scale. A 12 ounce tray contained 30 nuts for an average weight of 0.4 ounces each.
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Rooster testicles are like little sausages. The casings contain flesh with an appearance and texture similar to tofu. Connoisseurs like them barely cooked so they are very tender and even a little liquid in the center, and when you bite into them they kind of go "sploosh" in your mouth. The less experienced may wish to have them cooked a little longer so they have the texture of firm tofu all the way through.
The flavor is quite mild, kind of like tofu with overtones of chicken liver - pretty innocuous, once you get used to the idea of eating rooster 'nads.