And before anyone gets big ideas about the chloroform, it is not pure chloroform; it is generally contaminated by phosgene, which is truly terrible stuff.
Thanks to your comment I now know the other nights, where they were not rendered unconscious by blunt trauma, but rather through a rag of chloroform, they were probably inhaling phosgene too.
Those boys were sure putting their futures at risk!
IRL, that injury on either side is equally worrying.
It's probably five minutes of steady inhalation while your mouth and nose are covered by a rag (not held above your face).
Not particularly practical.
Source: my EMT class on poisons and ODs, thank you very much.