Macaque is onomatopoetic.

Emesis rhymes with rhesus, but yack rhymes with macaque.

Johnson, Hill and Cooper spent time with macaques, carefully noting when each individual animal vomited and whether it then reingested (for that is the technical term) whatever came up. All told, the scientists compiled "both quantitative and qualitative data on observations of 163 instances of vomiting from two groups of bonnet macaques in southern India". They used this data to "establish a conservative rate of vomiting in free-ranging macaques".

The rate is 0.0042 vomits per individual per hour. That's the conservatively high estimate, using data gathered by watching macaques who live near a temple on Chamundi Hill, a forested outcrop near Mysore in Karnataka. But it is not the whole story. Another group of macaques lives in the Indira Gandhi Wildlife Sanctuary, in Anaimalai Hills, Tamil Nadu. These forest-dwellers vomit at a different rate from their temple cousins: 0.0028 vomits per macaque per hour.

The scientists observed closely and keenly. Here is a typical passage from their report: "Only one adult female in the forest showed interest in another macaque's vomit; she twice smelled the mouth of an adult female. During observations at the temple, we saw 20 different individuals show interest in another's vomit on 21 occasions. Ten of the individuals were successful in eating some of it on 11 occasions. Of the individuals that ate or tasted another monkey's vomit, two were adult females, two were adult males, three were juvenile females, and three were infants."

Science!