Left: body part 月/肉, right: sunrise 旦 (sun 日 above the horizon 一)
Mnemonic
([Medically not fully correct, but:] Gallstones can cause nausea after eating or in the morning:) The body part you feel (already) at sunrise is: the gall.
The radical niku is typically at the left side of a composition and drawn as: 月, which looks equal to: "moon, month 月" but has the meaning 'body part'.
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