Rosa Bonheur created several animal portraits, giving pets the dignity of subjects, almost as if they were human. Her animals are never humanized, they are not caricatures, and do not have a political or satirical purpose (unlike those of many other animalist artists). Martin, a terrier is perhaps one of the most successful examples of Bonheur's animal portraits.

As is typical of portraits, the painting shows the name of the subject written in ordered red characters on the highest part of the painting. The artist's signature and the year are on the right instead, on the margin, painted with less meditated writing. Terrier dogs are hunting dogs and retain this instinct even when they are not used for this purpose. Their fur is characterized by different shades of brown, gray, white and black, to blend into the undergrowth or tall grass. The artist was able to perfectly capture the animal's fur, defining it with the finest touches of a brush, describing it in all its matted vitality. The dog looks at the observer in a severe and frowning way. Red and shiny eyes give it a sad, emotional tone. Bonheur's great ability was to provide the animal with individual characteristics, distinguishing it from the stereotypes of the breed.