Some cats easily perplexed (2,3)
I believe the answer is:
at sea
'perplexed' is the definition.
('at sea' can be similar in meaning to 'perplexed')
'some cats easily' is the wordplay.
'some' indicates a hidden word (some of the parts of the word are used).
'AT SEA' is hidden within 'cats easily'.
(Other definitions for at sea that I've seen before include "Bewildered on the ocean?" , "Worse things can happen here" , "'Filled with bewilderment (2,3)'" , "Voyaging" , "Might marines be" .)