The toddler at 21-month-old Juli learned to respond using the ASL word "yes". When I asked a yes-no question, I encouraged Juli to respond with a "yes" (ASL word, not a "nodding" gesture). Juli hasn't nodded yet, but she was able to sign "yes".
Whenever Juli asked for something that I reached for it and looked at her. Initially, she might reach out her arms or hands or something affirmative. I encouraged her to reply by signing yes.
The location parameter of the ASL word boy formed from the "20" handshape to the correct handshape (flat "O") which made the production all correct.
At the end of this week, I caught Juli producing waggling-tail using two-handed (with the dominance condition).
For the past few or more weeks, I noticed that Juli would bring my glasses to me in my bed in the mornings before she took my hand to "help" me get up.
In parallel, I noticed that Juli would sometimes walk around with partially closed eyes. Or, she simply squinted hard that her teeth flashed.
I didn't realize that these two things connected until now when Juli sometimes insisted me to put on my glasses at meal times. It appears that Juli thought I couldn't see well (or not at all) without my glasses.
The following referential words and phrases that Juli used this week: hello/hi (usually when approached an older kid), dad hug, (her excuse to get out of the crib), search, yes, some more shown in the video above, and other ASL words mentioned in the past months.