Not to deliver it, but to take the package or envelope, check the address, then put it in a pile to go to a distribution center in the appropriate, proximal zip code of its destination. That done, the mail might wait up to a day to be flown out, two days at times, then another day to be delivered by ground.
Some breeds of dogs have a natural curl or bend to their tails. But others have been selectively bred to take this curl to an extreme, cork-screw shape. Dog breeds with curly tails referred to as screw tails include Boston Terriers, Pugs, Bulldogs and French Bulldogs.
In both cases, the only thing that moved in the image was the tail. When dogs saw a dog image or silhouette wagging its tail to its right side, they stayed relaxed. But when they saw a dog wagging its tail to its left side, their hearts began to race and they looked anxious.