>>2309>just lazy animation
It's probably not that because it's like that in the manga, too.
However, in canon:
- Sakaki dislikes doctor offices
- Sakaki is very neat
- But she's bad at art. Even Osaka made better plushy-plushes
Therefore, headcanon: Sakaki neatly wrapped her own hand, in order to avoid going to the doctor. She did it neatly, but messed it up because she's bad at art. There, that's why she has two fingers wrapped together.