Photo: Sonny Radio - via Look At This 

While Dalmatians and Samoyeds are known for their natural warm smiles, any dog can learn this trick. With some patience and love from you, your dog will be showing their pearly whites in no time. 

Teach the dog the command sit before teaching it how to smile, and be sure that the dog is sitting before the lesson begins.

via wikihow

Dogs can be trained to discriminate.

It is possible to mitigate such behavior, through a sort of doggie diversity training, whereby the pet is gradually exposed to what sets it off. But it can be hard to persuade your black or white-bearded friends to participate in such cultural immersion exercises. (My friends had serendipitously hired a black trainer for Percy, whose behavior has since improved.) And even careful training can never totally eliminate the possibility that a trigger too similar to the traumatic event could cause the dog to lash out.

story via slate