Answer: subject
Step-by-step explanation:
A gerund is a noun formed by a verb root plus the present participle ing. A gerund phrase consists of a gerund and its modifiers or objects, it functions as a noun, and it can act as a subject, an object, or a predicate nominative.
In this example, the gerund phrase is "My screaming into the darkness," which functions as a subject noun and takes the third-person singular verb "attracted"