If you place a Lion, a Bengal Tiger and a Grizzly Bear into an exhibit, you will get a yellow brick path to use. The item description says "Yellow brick paths indicate to guests where they should walk, especially scarecrows, lions and tinmen"; a reference to The Wizard of Oz.
Placing a mermaid statue inside an aquatic enclosure will cause the statue to break, revealing an actual mermaid that was trapped inside. This mermaid counts as any other aquatic animal.
If a herbivorous animal is placed into an emperor penguin exhibit, the penguins will attack and eat the animal. After this occurs, the penguins will attack and eat any animal that is placed in their enclosure.