What is my mushroom doing?

[nanonoob0]

Hey all,

I've had my evo 13.5 fully stocked for about 4 months, and these guys (really this rock) were one of the first things in. I haven't added or changed anything recently, and today one of them started looking strange. Last night it looked like the bottom one, but much larger. Today when I got home from work its mouth was extended like this, and the rest folded back. Does anyone have an idea of what it is doing?

 

[Mayerlyn A]

Not sure what's going there unless it's splitting. That's a possibility