Look, a goose! (6)
I believe the answer is:
Here is my best explanation:
I believe this is a double definition.
'look' is the first definition.
(informal term for a look or glance)
'a goose' is the second definition.
(gander is a kind of goose)
(Other definitions for gander that I've seen before include "Male 7 across", "Male bird - look", "Male goose; look (colloq.)", "Goose sauce is good for it", "A butcher's -- bird", "Butchers - goose", "'What's sauce for the goose is sauce for the . . . . . .'", "male member of the Anatidae family", "Glimpse" and "Look; male goose".)