ok so I've been keeping a molly in with Lulu for a couple months- a friend moved away and left the molly in my keeping. I'd noticed he started slowing down a bit in the last few days and last night he seemed to be really struggling and I figured it was his time to go (molly was old) and I didn't want Lulu to pick on him or have him get sucked towards the filter- so I got Lulus little tub that she came in- put him in that with some food- and floated it in the tank so it would stay warm. getting out of the filter current actually perked him up some and he ate the food.
this morning I woke up and Lulu was inside the little cup with him and he was dead. She had squeezed through the little airhole on the lid- abut the size of my little finger- and she seemed very vexed about being stuck in that little cup. I took her out and will dispose of Molly- but I have no idea why she wanted to be in there. Maybe she was just curious? He was not eaten.
I didn't even think she could fit through that little hole. She is unharmed- seems happy to be free again.