tell her what mami?

I don't know, but I think Mami here should be happier. After all, she got to enjoy doing things together with those two since they approached her directly.

jasokun said:
tell her what mami?

Well, it could be one of the following:

1) Tell her that she 'knows'.
2) Tell her that the cake wouldn't taste good, since she knew what went into it.

Would be pretty interesting if she said that she is allergic to whatever is inside the cake.

She would not be able even to try...

jasokun said:
tell her what mami?

isn't that about that it IS NOT her birthday?

Mami could just say "I hope you make one for my birthday, it's in three months."

But that wouldn't be funny. Poor Mami.