A constant symptom is the increased secretion of saliva with a consequent frothing at the mouth, or the secretion may hang from the lips in long strings.
"Special Report on Diseases of Cattle"
U.S. Department of Agriculture J.R. Mohler
The water boiled about its nose, and suggested a frothing caused by the monster steed's expelled breath.
"The Frozen Pirate"
W. Clark Russell
Two men in an open boat at sea, their lips frothing with thirst, their eyes burning with famine, shall fall upon each other and fight to the death.
"The Frozen Pirate"
W. Clark Russell