Bracken always being in jail is probably a reference to “The Unicorn in Captivity”, a 15th-century tapestry which is the most famous unicorn artwork of all time
[ID: tapestry of a unicorn sitting in a field of flowers, in a small pen, collar around its neck affixed to a pomegranate tree.]
"The Unicorn in Captivity" may have been created as a single image rather than part of a series. In this instance, the unicorn probably represents the beloved tamed. He is tethered to a tree and constrained by a fence, but the chain is not secure and the fence is low enough to leap over: The unicorn could escape if he wished. Clearly, however, his confinement is a happy one, to which the ripe, seed-laden pomegranates in the tree—a medieval symbol of fertility and marriage—testify. The red stains on his flank do not appear to be blood, as there are no visible wounds like those in the hunting series; rather, they represent juice dripping from bursting pomegranates above. Many of the other plants represented here, such as wild orchid, bistort, and thistle, echo this theme of marriage and procreation: they were acclaimed in the Middle Ages as fertility aids for both men and women. Even the little frog, nestled among the violets at the lower right, was cited by medieval writers for its noisy mating.