Apothecary Alligator

"There was a large crystal ball with a crack in it, an astrolabe with several bits missing, a rather scuffed octogram on the floor, and a stuffed alligator hanging from the ceiling. A stuffed alligator is absolutely standard equipment in any properly-run magical establishment. This one looked as though it hadn't enjoyed it much."

- Mort

The workshop of a wizard, alchemist, or apothecary is never complete without a stuffed crocodile or alligator hanging from the ceiling. What it's actually for is anybody's guess.

The visual image may be inspired by early museums, "cabinet of curiosities" -- see this picture from 1655. Admittedly the alligator (or, more likely, crocodile) is hanging on the wall (at the right), but ceiling is well filled with specimens. Note that alligators are only found in the Americas and China.

Art

 * "The Alchemist at Work", painting by David Teniers the Elder

Literature
"There were tables strewn with archaic instruments of doubtful use, with astrological charts, with skulls and alembics and crystals, with censers such as are used in the Catholic Church, and volumes bound in worm-eaten leather with verdigris-mottled clasps. In one corner stood the skeleton of a large ape; in another, a human skeleton; and overhead a stuffed crocodile was suspended."
 * "The Return of the Sorcerer" by Clark Ashton Smith:

"There was a real corkindrill hanging from the rafters, very life-like and horrible with glass eyes and scaly tail stretched out behind it. When its master came into the room it winked one eye in salutation, although it was stuffed."
 * Merlyn's cottage in The Once and Future King:

"Gradually, the children discovered other treasures: a chart on which the signs of the zodiac were nicely touched up by Miss Price in water color; a sheep's skull; a chocolate box full of dried mice; herbs in bunches; a pot of growing hemlock and one of witch's bane; a small stuffed alligator, which hung by two wires from the ceiling. "What are alligators used for, Miss Price?" asked Paul. Again Miss Price's long training in truthfulness overcame her longing to impress. "Nothing much," she said. "They're out of date now. I like to have it there for the look of it.""
 * Miss Price's workroom in Bedknob and Broomstick by Mary Norton.

"The stuffed crocodile hanging from the ceiling; the leather-bound books, an astrolabe, convex and concave mirrors, odd scientific instruments"
 * Lord Portico's study in Neverwhere:

"Like all wizards' workshops, the place looked as though a taxidermist had dropped his stock in a foundry and then had a fight with a maddened glassblower, braining a passing crocodile in the process (it hung from the rafters and smelt strongly of camphor)."
 * Frequently mentioned, and Lampshaded as a occupational necessity, in the Discworld series. Every proper wizard has a stuffed alligator hanging from the ceiling of his laboratory, even if there aren't any alligators naturally in the area. No one, especially the wizards, is sure why.
 * The Light Fantastic:

"A mummified crocodile hung from the low rafters overhead."
 * Cutwell's workshop in Mort.
 * The dog wizard Tibbeth's shop in Stranger At The Wedding by Barbara Hambly:


 * An early edition of The Steerswoman by Rosemary Kirstein shows, on the cover, a scene set in a wizard's sanctum. You can tell it's a wizard's sanctum because of the stuffed crocodile hanging from the roof -- an interesting case of trope-as-shorthand, since the wizards' sanctum in the book itself is entirely bereft of taxidermied reptiles.
 * Mentioned in Book 1 of The Bartimaeus Trilogy in the description of the magician Arthur Underwood's study. Bart notes that this is a good indication that Underwood is distinctly second rate and trying to hide it; truly powerful magicians favor a sleek, modern look.
 * In "One Good Knight" (from the Tales of the Five Hundred Kingdoms series by Mercedes Lackey), one character comments that the Tradition requires Acadian magicians to have a stuffed crocodile hanging from their rafters. When he tried to get rid of his, there was an even bigger one hanging from his ceiling the next day, looking smug. Which makes one wonder how managed to hide the fact that he's a magician...
 * In The Wise Man's Fear, Cadaceus, who purports to be a healer, has one in his tower.

Tabletop Games

 * Call of Cthulhu (tabletop game) campaign The Fungi from Yuggoth, adventure "The Thing in the Well". Dr. Cornwallis has a stuffed alligator hanging by wires from the ceiling of his alchemical laboratory.

Theater
"And in his needy shop a tortoise hung, An alligator stuff'd, and other skins Of ill-shaped fishes"
 * The description of the apothecary's shop in Romeo and Juliet, Act V Scene I:

Video Games

 * The Voodoo Lady in The Curse of Monkey Island has a stuffed alligator whose tongue you have to pull to summon her.

Web Comics

 * In The Mansion of E, Crazy Rhid has a stuffed "crocogator" hanging in his chemical workshop.