D. R. MacDonald writes that the story of the baptized lion in the Acts of Paul is a case of a Christian revision of the well-known tale of Androcles and the Lion (The Legend and the Apostle, 21-22):
The Ephesus story is a Christian version of “Androcles [or, more corrrectly, Androclus] and the Lion.” …The story appears in the Attic Nights of Aulus Gellius (5.14; ca. 160 C. E.). Gellius borrowed it from Apion’s Aegyptiaca (first century C. E.), but no doubt the story originated in oral tradition. At the theater in Corinth, archeologists have discovered at the bottom of a wall enclosing the orchestra a series of painting sof human figures fighting with wild animals, under one of which is an inscription reading: “The lion recognizes the man under the bull as his savior and licks him.” Since the orchestra wall dates from early in the first century C. E., the tale apparently was popular lore by that time.
The citation of the inscription at Corinth is of doubtful relevance. The bull is an element that does not appear in the Acts of Paul. But more to the point, Apion never presented this story as “oral tradition” but rather as an event he saw with his own eyes. And why not? Is it so incredible that Apion, who visited Rome at the time of Gaius Caesar, could have attended a few of the circuses that were the mainstay of entertainment in Rome? The Romans were accustomed to watching the feeding frenzies of animals trained to devour human flesh. This was a part of the live entertainment that a visitor could also attend on a circus day in the world’s premier city. People did retell the story, to be sure. Apion says so (LCL, 1.427):
“Afterwards,” said he [i.e., Apion], “we used to see Androclus with the lion, attached to a slender leash, making the rounds of the shops throughout the city ; Androclus was given money, the lion was sprinkled with flowers, and everyone who met them anywhere exclaimed : ‘This is the lion that was a man’s friend, this is the man who was physician to a lion.’”
I personally doubt that Apion lied, by taking an oral story and pretended it was something that he himself had seen. It seems more likely to me that the back story which Androclus told was part of the show. I.e., there’s a sucker born every minute. Androclus claimed to have been a runaway slave who healed a lion of a thorn in his paw while hiding in Africa and to have lived three years in the cave on the food that the lion provided him. Afterwards, he grew weary of the food that the lion brought him, and he returned to civilization only to be arrested for being a runaway and condemned to die in the games. Then, the lion whom he had succored in the cave was the very same that they released against him. So he claimed.
The whole story was probably just a concoction and that Gaius Caesar was likely privy to the actual facts. Androclus was more likely a lion tamer and never a runaway slave. His leading the lion around the streets of Rome on a leash afterwards basically gives it away. Spectacles often have an element of deception in them, for people want to be shown a good time.