Short answer: no one knows for sure why dogs roll in dead animals, poop or garbage. Some ideas are below.
What the AKC says
The AKC says there is no definitive answer, and that wolves also roll in strong odors. One theory is that dogs roll to disguise their own scent, but the AKC points out flaws in that idea. Another is that they spread their scent, but dogs roll with their backs and shoulders, not scent glands. It says there is also a simpler possibility: dogs may roll in stinky things because they enjoy it.
What to do
Scan ahead on walks and call your dog away before they commit. See emergency recall, long line recall and a dog who eats poop.
Get the right help
If your dog also eats what they find, ask your vet.
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Sources
Sources & care notes
Frequently asked questions
Why do dogs roll in smelly things?
Nobody knows for sure. Wolves roll in strong odors too, and the theories each have their flaws.
How do I prevent the roll?
Scan ahead on walks and call your dog away before they commit to the prize.
What cue helps most?
A well-practiced recall, built with rewards, so calling away works even when the smell is tempting.
What if my dog also eats what they find?
Ask your veterinarian, since eating found items carries its own risks.
