Button Polyp Question

[kcstrad]

With water conditions aside, what causes this specimen to close and not reopen. Ive bought this twice, 1 year ago, which closed and never reopened and then last week, which was open when I put it in teh tank but the next day closed and has since stayed closed. Could this be the result of something nipping at it?

 

[Fatal Morgana]

It is possible that nipping is the cause, but usually it just close up for no appearant reason. I have some that closed for months, and it reopened without any intervention.