Flux has already implemented the expressions well, but some are missing and don't always look natural.
I implemented these facial expressions for you:
( sad )
( angry )
( scared )
( happy )
( surprised )
( disgusted )
You can use both tags and captions, both together and individually, my advice is to use the expression tag between parentheses before the caption.
You can also mark it by adding "very" to the expression in brackets, and with additional tags to add after the caption, such as "open mouth", "scream", "smile", "laugh", "terrified" etc.