Angelfish shaking their ventral fins ?!

[ch-b]

Sometimes my angelfish shake their ventral fins what does that means they are not fighting or kissing or anything just shake their ventral fins and sometimes their whole body what does that means?

 

[Pandicorn]

Perhaps they are just swimming, or just showing off. I can't vouch for angels since I've never owned them, but my GBR sometimes just kinda flick their fins at each other or other fish.