It’s believed that famed Underground Railroad leader Harriet Tubman mimicked the call of the barred owl to communicate with the freedom-seekers she was guiding. According to Ranger Angela Crenshaw of the Harriet Tubman Underground Railroad State Park in Church Creek, Maryland, hoot owls, as the nocturnal birds are also known, “make a sound that some people think sounds like ‘Who cooks for you? Who cooks for you?’” she told Audubon in a 2020 interview, in which she also referred to Tubman as “the ultimate outdoorswoman.”

In addition to owls, it’s thought that Tubman used other animal calls as cover signals, says Debra Campagnari Martin, the historic preservation planner for the City of Wilmington, and a board member and researcher for the Underground Railroad Coalition of Delaware.

When the Underground Railroad was in operation, the concept of train travel was still very novel, says Mullock. “This was new industrial technology at that time, and so even the [code words] that we think of now as [being] kind of obvious, were really novel ways of thinking about the routes,” she says. This includes referring to freedom-seekers as “passengers,” and the people like Tubman who guided them on the journey as “conductors,” she notes.

Along the same lines, passengers—who were also referred to as "baggage," "bundles of wood," "cargo" and "parcels"—traveled between safe houses on the route known as “stations,” which were owned by “station masters.” Others who assisted passengers on their way north were known as “agents.”

Though the specific terminology wasn’t necessarily consistent along the entire route, the wide range of experiences and situations that could be explained using language related to the railroad made translating messages relatively straightforward. “[The code words] were not standardized, but agents knew each other and understood,” says Martin.

There is evidence, including post-Civil-War court testimonies and historical records, to suggest that some people associated with the Underground Railroad referred to the Ohio River as the “River Jordan.”

As the country’s only physical boundary between the southern states, where slavery was legal, and the northern states of Ohio and Indiana, where slavery was prohibited, it held geographic as well as symbolic significance. In reality, though, the Fugitive Slave Acts could still be enforced in the so-called “free” states, which also didn’t guarantee any basic civil or political rights to their non-white residents. Plus, as Martin points out, the “River Jordan” wasn’t necessarily a code word exclusively reserved for the Ohio River. “This biblical reference was probably used for numerous rivers oriented towards free states or Canada,” she explains.

Formerly enslaved people, including Frederick Douglas, recalled singing religious folk songs known as “spirituals” while held in bondage. As Douglas writes in his 1855 book My Bondage and My Freedom, "A keen observer might have detected in our repeated singing of 'O Canaan, sweet Canaan, I am bound for the land of Canaan,' something more than a hope of reaching heaven. We meant to reach the North, and the North was our Canaan." Spirituals also served as an important method of communication on the Underground Railroad.

In interviews following the Civil War, Tubman said that she sang two spirituals—“Go Down Moses” and “Bound For the Promised Land”—while guiding freedom seekers north. “She would speed up or slow down the tempo to indicate whether it was good timing for someone to escape, or if there were dangers perceived,” says Mullock. However, apart from these two examples from Tubman, Martin says few other “conductors” ever disclosed the names of the spirituals.

Tubman also used coded references in messages sent by mail, says Larson. More specifically, she referred to another spiritual, “Old Ship of Zion,” in a coded letter that she had someone write on her behalf (she never learned to read or write) in Philadelphia, and sent to a friend in Maryland “just before she set out to rescue her brothers at Christmas 1854,” Larson explains. In the letter, Tubman requested that the recipient—a free Black man named Jacob Jackson—“read my letter to the old folks, and give my love to them, and tell my brothers to be always watching unto prayer, and when the good old ship of Zion comes along, to be ready to step aboard."