Yayoi seems to close her eyes happily ( smile!, like this -> q^ ^p ) at the end of "Kirame Kirari".
Haruka also closes her eyes (in cool way) in "I want".
Iori has a little evil smile ( like this -> q>.<p ) in "Futari no Kioku"
Generally speaking, every idol has her own way of singing and expression in each song with little nice details. This means there are at least 10 versions for each song in iDOLM@STER. This is why I like iDOLM@STER the most! XDD