in which mouth do people speak least?

in which mouth do people speak least?
英语脑筋急转弯
take one from nine and leave ten!what is it?
what shows different persons though it is thesame thing?
there's a note on the door of a manager ,on it is :IM2BZ2CU.what does it mean?

补充：
take one from nine and leave ten!what is it?
9
手写体的9和o加1差不多.
what shows different persons though it is thesame thing?
distorting mirror
哈哈镜
there's a note on the door of a manager ,on it is :IM2BZ2CU.what does it mean?
I'm too busy to see you.