Welcome to 3reef! Hope you are enjoying the hobby so far. Looks as if the food is to big for the nem. If it's to large they will spit it out that way it doesn't spoil in there stomach. They really only need very small pieces. I'm not expert on nems, or any coral as I am new to this hobby as well. Maybe someone with a lot more experience will give better advicd. And as far as a chocolate chip star as far as I know they are not reef safe. Not sure how it will act with a nem. But I do know they will eat soft coral like zoas and things like that.