goose
鵞 centers on a goose, a large waterbird. The meaning is straightforward and specific to this animal.
鵞 combines 我 (which may contribute a phonetic element) with 鳥 (bird), forming a character for a specific bird, the goose. The exact historical development is uncertain, but it is likely a phono-semantic compound.
The top part 我 looks like a proud, upright figure, and the bottom 鳥 is a bird. Picture a goose standing tall and honking loudly: 鵞 is that goose.
For ガ, imagine a goose honking "GA!" as it chases you. The loud "GA" sound cues the reading ガ.
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