Watch them taking rest inside and become irritable (6)
I believe the answer is:
snappy
'irritable' is the definition.
(I know that irritable can be written as snappy)
'watch them taking rest inside and' is the wordplay.
I cannot really see how this works, but
'rest' could be 'nap' (a nap is a short sleep) and 'nap' is present in the answer.
'watch' could be 'spy' (spy can mean to watch or see) and 'spy' is found within the remaining letters.
This accounts for all the letters.
This explanation may well be incorrect...
'become' is the link.
Can you help me to learn more?
(Other definitions for snappy that I've seen before include "Stylish - brusque" , "Irritable, curt; stylish" , "Irritable, curt; concise" , "Short-tempered" , "Ratty" .)