"Fudge!" (4)
(Other definitions for rats that I've seen before include "(Hunts) rodents - expression of irritation" , "Snoopy's imprecation - vermin" , "Rodent pests" , "Oh no" , "First word of 'The 21 19'" .)
'fudge' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for drat that I've seen before include "Mild expletive" , "that expresses annoyance" , "Bother" , "Exclamation of annoyance" , "Informal expression of annoyance" .)
(Other definitions for darn that I've seen before include "Mend with 17s - mild expletive" , "Repair with wool" , "Repair (sock)" , "Blow" , "Mend (e.g. socks)" .)
'fudge' is the definition.
(I know that fudge can be written as falsify)
This is the entire clue.
(Other definitions for falsify that I've seen before include "Alter in order to deceive" , "Counterfeit" , "Forge; misrepresent" , "Alter so as to mislead" , "Cook - distort" .)