feedback control?

I've noticed the following circuit in a screwdriver, and I'm wondering what purpose does the "extra" line do. I imagine it is some sort of feedback control. I know a parallel cap across the motor shunts high frequency noise. NOTE: the equal characters are capacitors.

    to connector
    |
    |------+--+
    |      |  |
/-------\  |  =
| Motor |  =  |----- to connector
\-------/  |  =
    |      |  |
    |------+--+
    |      
    to connector

Extra line usually connected to ground, the same EMI suppressor role

Thanks that makes sense.