<sod>[[Snake venom|Venom in snakes]] and some [[lizard]]s is a form of [[saliva]] that has been modified into [[venom]] over its evolutionary history.<ref>{{cite web|title=Reptile Venom Research|url=http://www.reptilepark.com.au/venom_snake.asp|publisher=Australian Reptile Park|accessdate=21 December 2010}}</ref> In [[snake]]s, venom has evolved to kill or subdue prey, as well as to perform other diet-related functions.{{sfn|Casewell et al.|2013}} <eod>
<sod>[[Snake venom|Venom in snakes]] and some [[lizard]]s is a form of [[saliva]] that has been modified into [[venom]] over its evolutionary history.<ref>{{cite web|title=Reptile Venom Research|url=http://www.reptilepark.com.au/venom_snake.asp|publisher=Australian Reptile Park|accessdate=21 December 2010}}</ref> In [[snake]]s, venom has evolved to kill or subdue prey, as well as to perform other diet-related functions.{{sfn|Casewell et al.|2013}} The evolution of venom is thought to be responsible for the enormous expansion of snakes across the globe.{{sfn|Fry et al.|2012}}{{sfn|Wuster et al.|2008}}{{sfn|Lomonte et al. (a)|2014}}<eod>