en , ▁origin ate ▁from ▁v ibr ations ▁of ▁thick ▁vocal ▁fol ds ▁in ▁the ▁l ary nx ▁of ▁the ▁cat . ▁Sound ▁production ▁is ▁facil itated ▁by ▁the ▁low ▁threshold ▁pressure ▁required ▁to ▁oscill ate ▁the ▁vocal ▁fol ds , ▁and ▁low ▁gl ott al ▁resistance . ▁The ▁rough - s ounding ▁quality ▁of ▁the ▁low - p itch ed ▁vocal izations ▁is ▁likely ▁generated ▁by ▁the ▁complex ▁pattern ▁of ▁vocal ▁v ibr ations , ▁caused ▁by ▁the ▁exc itation ▁of ▁multiple ▁modes ▁of ▁oscill ation ▁simultaneously . ▁Pr ust en ▁also ▁involves ▁air ▁being ▁ex h aled ▁through ▁the ▁nose ▁at ▁the ▁same ▁time ▁as ▁through ▁the ▁mouth . ▁This ▁may ▁represent ▁an ▁evolution ary ▁shift ▁from ▁exclus ively ▁l ary n ge al ▁vocal izations ▁to ▁mixed ▁nas al ▁and ▁l ary n ge al ▁sound ▁production ▁in ▁the ▁fel id ▁species ▁that ▁display ▁the ▁behaviour . ▁ ▁Sound ▁properties ▁ ▁Ph on et ically , ▁pr ust en ▁var ies ▁by ▁species , ▁however ▁the ▁basic ▁struct ural ▁pattern ▁remains ▁constant . ▁More ▁struct ural ▁similar ities ▁occur ▁between ▁the ▁two ▁le op ard ▁species , ▁and ▁also ▁between ▁the ▁t iger ▁and ▁j agu ar . ▁Ind ividual ▁sound ▁p uls es ▁are ▁more ▁separated ▁in ▁the ▁le op ards ▁in ▁comparison ▁to ▁the ▁other ▁species , ▁in ▁which ▁they ▁tend ▁to ▁be ▁more ▁closely ▁merged . ▁P uls es ▁may ▁occur ▁in ▁pairs , ▁in ▁which ▁a ▁bas al ▁pul se ▁and ▁an ▁upper - range ▁pul