Board Thread:News and Announcements/@comment-24934890-20181008004211/@comment-33287020-20181015163736

Except when Yang explicitly said Ruby couldn’t talk yet when Summer died, which contributed to her loneliness.

From Alone Together:

“My mom left me. Ruby's mom left too. Tai was always busy with school and Ruby couldn't even talk yet. I had to pick up the pieces. I had to keep things together. Alone. (pause) Weiss, if you have something to say, then say it.“

Kids say their first word around the age of 12 months, and they usually develop a bigger vocabulary by 24 months. Point being, when yang says ruby couldn’t talk yet, that means she was super, super young, and definitely not able to remember things.