Interaction in which one organism lays its egg in the nest of another organisms is called `ul(x)`. For example `ul(y)`.

Answer

### Step-by-Step Solution:

1. **Identify the Interaction**: The question describes an interaction where one organism lays its eggs in the nest of another organism. This is a specific type of ecological interaction.

2. **Define the Term**: The term for this interaction is known as "brood parasitism." In brood parasitism, one species (the parasite) relies on another species (the host) to raise its young.

3. **Explain the Mechanism**: In brood parasitism, the parasitic organism lays its eggs in the nest of a host species. The host then unknowingly raises the young of the parasite, often at the expense of its own offspring.

4. **Provide an Example**: A well-known example of brood parasitism is the relationship between the cuckoo bird and the crow. The cuckoo lays its eggs in the crow's nest, and the crow raises the cuckoo chicks as if they were its own.

5. **Summarize the Answer**: Therefore, the answer to the question is:
- X = Brood parasitism
- Y = Cuckoo (as an example of an organism that exhibits this behavior).

### Final Answer:
- The interaction in which one organism lays its egg in the nest of another organism is called **brood parasitism** (X). An example of this interaction is the **cuckoo** (Y).

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