In fact, she is not speechless. I have said it before, she is pretending. 

Every night, when I was concentrating on doing my homework, she would always stand silently behind me, sucking on her index finger that was peeling from saliva, staring at me blankly, expressionlessly, without blinking, like a soul, exuding a cold and damp breath. 

When I noticed and turned to look at her, she would take out her index finger, rub it on her pants, then grin, point out the window, and whisper, "Sister, there's someone outside." 

"Sister, there's someone outside." This was the only thing she would say after she became stupid, and she only said it in the dead of night, to me alone. 

Sometimes, to prevent her from saying this, I would sacrifice my reputation as a good student and go straight to bed without doing homework. Even then, she would appear by my bedside like a ghost, shaking me awake with her wet fingers. In the darkness, her childish voice was like a ghost: "Sister, there's someone outside." I knew there couldn't be anyone outside, because I lived on the fourth floor. Outside, there was only a large locust tree and the power lines strung above it. 

When my sister first started saying this, I fell for it countless times. I'd draw back the curtains, open the windows, and gaze at the swaying locust trees and the listless sparrows on the power lines in the empty night sky. Whenever I solemnly told her there was no one outside, she'd just giggle, her fingers between her fingers, drooling. 

At first, I assured my parents that my sister wasn't stupid, wasn't aphasic, that she was just pretending, deliberately acting out because she'd spoken to me. 

But my parents didn't believe me. They just frowned, tears welled up in their eyes, and sighed repeatedly, their expressions filled with disappointment and distrust. Then they'd hug my sister and wipe away her tears. 

Every time this happened, my sister would put her arm around my mother's neck and flash me a triumphant smile. 

Okay! You win, I accept it. But my sister, triumphant, didn't give up. Every night at ten o'clock, rain or shine, she'd appear before me, pointing out the dark window and repeating the same words. It seemed as if her only purpose in life was to constantly play these unskilled, clumsy pranks on me. 

Yes, until that day, I had always believed that, always thought it was all my sister's prank. That noon, all the students who weren't going home for lunch were slumped over their desks, drooling and dozing. The electric fan in the classroom was turning dully. 

I had finished my afternoon homework and was just about to take a short nap when my deskmate, who had been hunched over his desk reading, suddenly looked up. From resting his head on the desk for so long, a red mark appeared on his forehead, a strange look. His eyes were also strange, almost filled with fear. 

He whispered to me, "Do you believe in ghosts?" 

I shook my head, "The teacher said we're materialists, and there are no ghosts in this world." 

"Is everything the teacher says right?" He placed the magazine on the table. The cover featured a ghostly female ghost, with glassy eyes and an expressionless face, who bore a striking resemblance to my sister. 

My deskmate swallowed and continued, "I just read a story that said children under the age of six can see things that adults can't, namely ghosts. The child in this story saw his mother, who was killed by his father, lying on his father's back. So he always said to his father..."