Here's why:
* Direct Object: The direct object is the thing that receives the action of the verb. In this case, the puppy is the direct object because Amanda bought it.
* Indirect Object: The indirect object is the person or thing that benefits from the action of the verb. In this case, "us" benefits from the action of buying the puppy.
The sentence could be rephrased to emphasize the indirect object: "Last week Amanda bought a puppy for us."