yeah,maybe for the 3dr times she will find the truth and conan will find a trick to make her believe she's wrong

great...
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^^" Let's be fair with Ran, Shinichi made her time though.
MAYBE SPOILERS?
1. When she first found out, she confronted him, but gave herself right away, so Shinichi could get the help of Agasa and I think it is quite believable (does this word even exist?) that she could be tricked by hearing Shinichi's voice and seeing at that time Conan.
2. Ran found out Shinichi's secret again (volume 14), she manage to keep it to herself so Shinichi couldn't think of a backplan and was only saved by Yukiko.
There should be noted that Ran still had her doubts, Yukiko's act was not so convincing and she became 100% sure of Conan's true identity...
3. Ran didn't confront Shinichi like in the previous two cases, she used "psychological
terror pressure" and it almost worked, hadn't Ai came up with a very convincing idea, and Shinichi, the real was seen together with Conan in Desperate Revival.
Even after this, Ran spoke about "I wish you were Shinichi" and stuff and then...
4. She again began to think that Conan is too smart for his age and she had a complete idea why was Conan so smart at the crime scenes, because Shinichi helped him. But Ran then realized that Conan didn't contact Shinichi ergo he is as smart as Shinichi, meaning he is Shinichi. And again, she thinks Shinichi tricked her, because he is sneaky. This time Ran gave herself away again and left an opportunity for Shinichi to take counter measures, and he tricked her with the phone. Which was convincing again, because even Ran thinks that she is paranoid, and she rather thinks that she is wrong in order to avoid disappointment in Shinichi. Also this time she looked for concrete evidence to corner Conan.
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I hope the last step will be the fingerprint-proof. And I do hope Shinichi won't get away with it. The police /Takagi/ has Conan's fingerprints and probably Shinichi's too, since he was in so many cases and in Shiragami case, they actually prooved that Shinichi si Shinichi with fingerprints.
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Anyways I don't think Ran is stupid because she can't figure out Shinichi's true identity. And for the plot's sake it cannot be revealed to her yet. It may be boring, but it is logical that his identity can't stay revealed in front of her till the end-parts.