Odd One Out Explanation:

Chicken
- Chickens are birds that lay eggs, have feathers, and are warm-blooded.
- They are different from the other options as they are not reptiles like snakes, tortoises, and frogs, or waterfowl like swans.

Snake
- Snakes are reptiles that lack limbs and eyelids. They also have scales and can be venomous or non-venomous.
- They are similar to tortoises and frogs in being reptiles but are different from birds like chickens and swans.

Tortoise
- Tortoises are reptiles with a hard shell covering their body for protection. They are known for their slow movement and herbivorous diet.
- They share the characteristic of being reptiles with snakes and frogs but are different from birds like chickens and swans.

Swan
- Swans are waterfowl that belong to the Anatidae family. They are known for their long necks, graceful movements, and loud honking calls.
- They are similar to chickens in being birds but are different from reptiles like snakes, tortoises, and frogs.

Frog
- Frogs are amphibians that have smooth, moist skin and lay eggs in water. They undergo metamorphosis from tadpoles to adults.
- They are different from birds like chickens and swans but share the characteristic of being non-reptiles with snakes.