Why does my hammer coral have a bubble?

[aquatics4life]

My hammer coral has had what looks like an inflated polyp for the past several weeks. It hasn’t grown or shrank really.

What is it and how do I help it?

 

[Reefwild]

Looks like it's ready to split imo

 

[aquatics4life]

Looks like it's ready to split imo

Yep it split into 4 heads.