Possible issue with a fungia

[Step Johns]

So a couple of days ago one of my fungias stopped puffing out as much as the others and got a black bit at the tip of its mouth. It still eats mysis but doesnt close its mouth all the way. I was wondering if anyone can help me with finding out what this is or how to fix it.

 

[DashTrash400]

Poop. It's fine my corals do it every now and again. Cut back on the feeding for a few days and it will go back to normal. My 2 cents at least.

 

[Step Johns]

I thought it was poop at first too but now im not sure. It has since closed its mouth but there is still a black bump at the top. I was sitting here looking at it with the lights off and it looks very much like a snail shell.