Such inventions had spawned concern that people from Phyle A might 
surreptitiously introduce a few million lethal devices into the bodies of 
members of Phyle B, providing the technically sweetest possible twist on the 
trite, ancient dream of being able instantly to turn a whole society into 
gravy. A few inroads of that kind had been made, a few mass closed-casket 
funerals had been held, but not many. It was hard to control these devices. If 
a person ate or drank one, it
might end up in their body, but it might just go into the food chain and get 
recycled into the body of someone you liked. But the big problem was the host's 
immune system, which caused enough of a histological fuss to tip off the 
intended victims.