Viewed part of the act, say (4)
I believe the answer is:
seen
'viewed' is the definition.
(to view is to see)
'part of the act say' is the wordplay.
'part of the act' becomes 'scene' ('scene' is part of 'act').
'say' shows a homophone (sound like).
'scene' sounds like 'SEEN'.
(Other definitions for seen that I've seen before include "Espied" , "Witnessed" , "watched" , "Sighted" , "Observed or percieved" .)