[@Masaki Haruna] Dion's mostly right, with the caveat that "Battle Speculation" also gives off faint pulses of chakra through the strings that act as a form of echolocation. Ria could possibly see the strings, though it'd be harder depending on how thinly Senhime chooses to weave them, and obviously distance is a small factor (but we're talking about the Sharingan here). It's entirely possible for others to see the strings too if Senhime makes them thick enough, but obviously they're gonna have to tread a little more lightly.