They are highly intelligent dogs which from a long time breeder told me once they are as smart as a 3 or 4 year old. (pethelpful.com)
Even if I spent 2 or 3 hours with the pups, it's a drop in the bucket compared to the amount of time the breeder spent with them. (americanshihtzuclub.org)
Over time breeders developed them into dogs with shorter legs, so more suitable for digging. (dogs.animal-world.com)