cut your nails vs cut your mouth

[keannu]

"cut" seems to be dubious. In 1, it means "cut off" your nails, but in 2, it means "scratched by something to bleed", not "amputating your mouth". So what's the difference between "cut" and "cut off" ?

jo3-2
ex1)...For example, in Korea, they say you should not cut your nails in the dark...
ex2)...He cut his mouth...

 

[Rover_KE]

Your dictionary should have told you that (amongst other things) cut ​can mean 'shorten with a sharp implement' (ex1) and 'wound with a sharp implement (ex2).

The prepositional phrase cut off means 'remove with a sharp implement' (as in 'all his hair').

Rover

 

[emsr2d2]

Technically, we "trim" our nails by cutting the top part of them off.