This is the 1001st most frequent Japanese word.
謎
Mystery; riddle; enigma.
The word '謎' refers to a mysterious circumstance or puzzle about the incident.
その事件はまだ解けていない謎のままです。
The incident remains an unsolved mystery.
Here, '謎' indicates an enigmatic quality or subtle mystery in her words.
彼女の言葉にはいつも少し謎が含まれている。
Her words always contain a bit of enigma.
In this usage, '謎' represents a puzzling or unclear meaning behind the painting.