Name mammal that lays egg.

Explanation

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks for a mammal that lays eggs. Most mammals give live birth, but there are exceptions.

2. **Identifying Egg-Laying Mammals**: Among mammals, there are two main groups: monotremes and therian mammals. Monotremes are the only group of mammals that lay eggs.

3. **Naming the Mammal**: The most well-known egg-laying mammal is the duck-billed platypus. It is a unique species that belongs to the monotreme group.

...