Dogs can eat avocado flesh, if they like it, without problems. The reason some say not to give avocados to dogs is because avocados are known to contain a toxin called persin, which is quite dangerous to other animals like horses and birds but is in fact harmless to dogs in small amounts. Avocados hold the highest concentrations of persin in their leaves, thick skin, and pits; avocado flesh contains low levels of this chemical a negligible amount for most humans, and for most dogs too. We don't eat the leaves, skin, or pits of avocados, so don't give these to your dog. A few thin slices of fresh avocado over your dog's dinner, or as a nutrient-rich treat, however, will be fine for your dog, unless of course he has a food allergy to it.