Speak to Lod

Walkthrough
When the Dragonborn first arrives in Falkreath, one of the guards will ask if a dog was seen running around the area. He will then suggest speaking to Lod, the local blacksmith who has lost his dog.

Speak to Lod
After locating the blacksmith, the Dragonborn can ask about the dog. Lod then explains that he is interested in finding the "fine, strong creature that's been wandering near town" and gives the Dragonborn some Fresh Meat to lure it. (A quest marker is also added to the map indicating which way to begin the search for the dog.)

Find the dog outside Falkreath‏‎
Proceeding towards the marker, the Dragonborn will quickly meet Barbas, a talking dog.

The encounter launches the more epic quest, A Daedra's Best Friend.

Sprich mit Lod