Dog-tongue or houndstooth is a flowering herb sometimes used for medicinal purposes. Since it grows in Old Woman Swamp, where the narrator and his little brother Doodle like to spend their time, they decide they will later earn their living picking it and selling it.

This is part of a longer youthful fantasy the two boys engage in. They want to live by the swamp, build a house of leaves, and have "swamp birds" for chickens. They wish to swing through the cypresses on vines and sit under an umbrella tree when it rains. This dream of living as children of the wild shows their love of nature and their love of their home. It also illustrates that they are attached to each other and can't imagine being separated as adults. Doodle even wants them to marry their parents so they can all be together, showing him as young and innocent.

What does "dog tongue" mean in "The Scarlet Ibis"?

During Doodle's discussions with his big brother about their future together, they talked of living in Old Woman Swamp, where they would build a house and live together. Doodle planned to "marry Mama" while his brother could marry Daddy. Doodle's plan also called for the boys to "pick dog-tongue for a living." Dog's-tongue is another of the unusual plant species mentioned in the story (which is presumably set in author James Hurst's home state of North Carolina). Also known as "Hound's Tongue," it is a "biennial weed (officially known as Cynoglossum officinale) with soft, tongue-shaped leaves" which gives off an offensive odor. Dog's Tongue "bears nutlets covered with barbed or hooked prickles." The root of the plant has been used as a remedy for coughs, head colds, and shortness of breath. The leaves have also been used, when boiled in wine, as a cure for dysentery.