Here is a picture of a part of a circuit, which contains a right leg driver.

My understanding of DRL is a circuit which send a signal to a human body, therefore this human body would have the same 'common voltage' as the circuit, which helps to increase CMRR.

However, I would like to know how the below DRL works, especially at the point A, B and C.

Also I have seen quite a few of DRL circuits, and they all do some sort of filtering (Low pass filter), I would like to know what value of cut off freq is aiming actually.