"It's easy to say those words. But do you really understand their weight? This is a world of secrets and death that you're stepping into. You might already have a foot in the doorway, but once you're in, you can't step out. Are you really prepared to die? To watch people around you die because you knew the wrong secret?"

Haibara honestly doesn't think Ran will even consider the option. She knows her well enough for that. She's as stubborn as Kudo.

But she doesn't trust Kudo to have delivered this message. Not with the weight it deserves. As smart as he is, as much as he relies on reason, when it comes to Ran, he's nothing but emotions. His explanations would be bogged down by his worries, his need to explain himself... and honestly, if Ran caught him and found out the secret, then their conversation probably happened just after transformation. Haibara knew from experience what that felt like.

In short, Haibara is the one who needs to make sure she knows what she is getting involved in. Her words were sharp, much sharper than a child's.