- Who
- Unknown
- Where
- ()
The rarest speech sound is `rÆ' in Czech and described as a rolled post-alveolar fricative. It occurs in very few languages and is the last sound mastered by Czech children.
 
In the southern Bushman language !xo there is a click articulated with both lips, which is written Â. This character is usually referred to as a `bull's-eye' and the sound, essentially a kiss, is termed a `velaric ingressive bilabial stop'. In some contexts the `l' sound in the Arabic word Allah is pronounced uniquely in that language.
