What does にへら mean when beginning a sentence?


For context, the sentence is にへら、という気の抜けた笑顔。 And the sentence before is
そこまで考えて、胸内にふと一人の人物の顔が浮かんだ。 The character whose monologue this is is spacing
out during a movie thinking about his recent past, if it helps.

Could someone help me understand what にへら means? I looked it up and only found
a Japanese question about にへら but it was in the middle of a sentence, so I
didn’t think it applied.




It's a mimetic word that describes a type of a happy and relaxing smile. へらへら
and にんまり are much more common, and にへら comes somewhere between them. You can
see 200+ illustrations tagged with にへら顔
[here](http://seiga.nicovideo.jp/tag/%E3%81%AB%E3%81%B8%E3%82%89%E9%A1%94?sort=clip_count).
If I can choose one, [this picture](http://seiga.nicovideo.jp/seiga/im8555356)
exactly matches my image of にへら.




It's a mimetic word that describes a type of a happy and relaxing smile. へらへら
and にんまり are much more common, and にへら comes somewhere between them. You can
see 200+ illustrations tagged with にへら顔
[here](http://seiga.nicovideo.jp/tag/%E3%81%AB%E3%81%B8%E3%82%89%E9%A1%94?sort=clip_count).
If I can choose one, [this picture](http://seiga.nicovideo.jp/seiga/im8555356)
exactly matches my image of にへら.

