A very mild slap across the face>
You start with original slap, then hit the face again on the backhand.
It originates from the tail action from a "salmon" whilst it swims
Invented in Duluth, MN, the salmon is a form of a high five/hand shake where one participant puts his hand and forearm next to another participants forearm and hand. The participants continue to slap their arms on eachother while sliding down the forearm to the hand in which they end in a high five.