Who Says Dogs Can’t Cry?

I've always heard that humans are the only animal able to cry.  But after seeing this video I have to say, I'm not convinced.

In a heart wrenching video a mother dog is shown after she and her pups were rescued and re-united with each other.

Tears stream down her face as she cuddles up to them again.

What do you think? Is this mother crying for joy after being re-united with her pups? Or is there just a lot of dust in the air?