Look, a goose! (6)
I believe the answer is:
Here is my best explanation:
This clue is a double definition.
'look' is the first definition.
'a goose' is the second definition.
(gander is a kind of goose)
(Other definitions for gander that I've seen before include "Male goose - quick look", "Male bird - look", "Glimpse", "Male goose; look (colloq.)", "male member of the Anatidae family", "Look; male goose", "Ranged over the bird", "'What's sauce for the goose is sauce for the . . . . . .'", "Butchers - goose" and "Bird from Newfoundland airport".)