Strange electric phenomenon? I don't understand this

[Splash1]

We always connect one end of the circuit to a positive pole and the other end to the negative pole of the battery.

But... When I connect 2 negatives poles or 2 positives poles using the next configuration... The motor works and the light bulb shines.

ONE END OF THE LIGHT BULB -(battery1)+-(battery2)++(battery3)- SECOND END OF THE LIGHT BULB

As you can see, the light bulb is connected to 2 NEGATIVE poles...
Why can I light a light bulb using 2 (negative or positive) poles?

 

[Nigel Goodwin]

You've got three batteries, two cancel each other out, so you're running off just ONE battery.

 

[crutschow]

As Nigel stated if you measure the voltage you'll see the voltage of one battery.