List three peculiar characters of mammals.

Explanation

### Step-by-Step Solution:

1. **Presence of Hairy Exoskeleton**: One of the most distinctive features of mammals is the presence of hair or fur on their bodies. This characteristic is not found in other classes of animals and serves various functions, including insulation, protection, and sensory perception.

2. **Mammary Glands**: Mammals possess mammary glands that produce milk to nourish their young. This feature is unique to mammals and is crucial for the survival and development of their offspring, providing them with essential nutrients during the early stages of life.

3. **Viviparous Reproduction**: Most mammals are viviparous, meaning they give birth to live young rather than laying eggs. This direct method of reproduction allows for a more complex development of the offspring within the mother's body, providing them with a safer environment until they are ready to survive independently.