Answer:
Tune; head.
Explanation:
In English language, a subject can be defined as the person, thing, idea or place that performs an action.
On the other hand, an object refers to the person, thing, idea or place that receives an action performed by the subject.
Also, a direct object is the specific thing a subject acts upon and as such it answers the question of what, whom or who.
In the sentence "Kristen Schaal hummed a tune and tapped her head at the same time." the direct objects are tune and head.
Kristen Schaal (subject) hummed (verb) a tune (direct object) and tapped (verb) her head (direct object) at the same time.
