A joke in the traditional manner

Did you hear about the mustard-fetching dogs?

No spoilers. The punchline is in the comments.

More jokes in the traditional manner
The Autobahn : Did you hear about the cow coloratura? : Did you hear about the thieving produce clerk? : Elementary school : A Golden Retriever : How did Bela Lugosi know what to expect? : How did Samuel Clemens do all his long-distance traveling? : How do amoebas communicate? : What did the doctor tell his forgetful patient to do? : What did the plumber do when embarrassed? : What happens when a senior citizen visits a podiatrist? : What is the favorite toy of philosophers’ children? : Which member of the orchestra was best at handling money? : Why did the doctor spend his time helping injured squirrels? : Why did Oliver Hardy attempt a solo career in movies? : Why did the ophthalmologist and his wife split up? : Why does Marie Kondo never win at poker? : Why was Santa Claus wandering the East Side of Manhattan?

[“In the traditional manner”: by or à la my dad. He gets credit for all but the cow coloratura, the produce clerk, the amoebas, the toy, the squirrel-doctor, Marie Kondo, Santa Claus, and this one. He was making such jokes long before anyone called them “dad jokes.”]