Sakura couldn't see this attack coming, but she was able to react: The only reason why this happened is because she was playing possum and Sasori took the bait and attacked with a simple frontal attack. She wasn't able to see it, but she damn sure was able to hear it considering the weird noises puppets make.
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She did this without help: Because Sasori was focusing on finishing Chiyo and payed no mind to Sakura, so obviously this left him open to an easy counter.
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Evasion: She evaded a few puppets out of a hundred that were being controlled by his chest, not his fingers...Chiyos ten puppets were having no problem taking them out, so obviously Sasoris puppets were not being controlled on the same level. Quality over quantity. You can see a huge difference between when Sasori was controlling the Kazekage puppet and stalemated with Ma & Pa to when he was controlling the 100 puppets.
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Chiyo and Sasori praised her evasion skills and strength: You said Sasori praised her evasive skills, i see no such thing. What I do see is, Sasori making fun of Sakura...
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