The most unique aspect of the Bushmen languages is the clicks.
Click sounds, which are found only in Africa as parts of
words, involve a 
sucking
action by the tongue, but the position of the tongue and the
way in which air is released into the mouth vary; thus clicks
may be dental, alveolar, alveolo-palatal, cerebral, lateral,
labial, or retroflex; voiced, voiceless, or nasal; aspirated
or glottal.
These clicks are represented by:
"/" The "first" click (dental), sounds like
"tsk, tsk! " and is made by putting the
tongue just behind the front teeth.
"≠" The" second" click (alveolar) ,
is a soft "pop" made by putting the tongue
just behind the ridge back of the front teeth.
"!" The "third" click (alveolo-palatal),
is a sharp "pop" made by drawing the
tongue down quickly from the roof of the mouth.
"//" The "fourth" click (lateral), is a clucking
sound like that made in English
to urge on a horse.
6 types of click sounds are known in all the Bushmen languages
but it's unlikely that any single language has all of them.
Some Bantu languages, notably Zulu and Xhosa, have borrowed
click sounds from the San languages.
