Follow her close; give her good watch, I pray you. (4.5.6)
Ophelia's mad ramblings are super problematic to the royal court, as we see here when Claudius orders Horatio to keep a close eye on her. The fact is that Ophelia's babblings about her father's murder could have important political implications. Later, we see just how volatile the realm can be when Laertes leads a rebellion and finds many eager supporters who would help him overthrow King Claudius.