Rolling your tongue into a longitudinal tube (U-shaped). This is generally said to be a trait inherited by a dominant gene -- if you can't roll your tongue, you have two recessive genes. However, there is little experimental evidence to support this, and multiple twin studies have found that identical twins do not tend to share this trait. This ability is most likely random, with no genetic inheritance involved. About 36% of humans can't roll their tongues.

Cloverleaf tongue folding is a separate trait/ability, and is somewhat more rare.

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