During his expedition, Walker gained the trust of the Arumbaya's, who showed him the Heart of the Jungle, an ancient gemstone sacred to the Arumbayas, who claimed it to have magical medicinal purposces. Walker's local San Theodoran guide, Lopez subsequently stole the gemstone and hid it in the Idol of the Broken Ear, which was, ironically, a gift to Walker in honour of his vow of silence about the gem. The Arumbayas gave chase to Walker's expedition after learning it had been stolen, but Lopez panicked and fled before the Arumbaya's attacked, leaving Walker with the idol, who would bring it to Europe.
Long after Walker returned the fetish would eventually come to rest at the Museum of Ethnography in Brussels. He would also later recollect his experiences in his book Travels in the Americas, published in London in 1875. Walker was only mentioned in The Broken Ear, but was featured in a flashback tale of Dr Ridgewell translating the story of Walker's visit to Tintin as told by the Arumbaya chieftain in The Broken Ear (TV episode).