LESS OR FEWER?

One of Stannis Baratheon's pet peeves is being a major grammar Nazi.
Or, at least, correcting the linguistic mistakes made by others. Especially when it comes to whether it should be "less" or "fewer":



Davos: And it's four less fingernails to clean. 
Stannis: Fewer. 
Davos: Pardon? 
Stannis: Four fewer fingernails to clean.