goose
鵝 centers on a goose, a large waterfowl. The meaning is straightforward and specific to this bird.
鵝 combines 我 (which likely contributes a phonetic element) with 鳥 (bird) to denote a goose. The exact historical development of the phonetic role is uncertain.
The left side 我 (oneself) and the right side 鳥 (bird) together suggest a bird that is self-important or proud, like a goose strutting around.
For ガ, imagine a goose honking a loud 'GA!' as it chases you: GA -> ガ.
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