Under 14 CFR § 107.39, a remote pilot may operate a small unmanned aircraft directly over a non-participating human being only if —

Why: 14 CFR § 107.39 permits operating over a human being only if that person is directly participating in the operation, is under a covered structure or inside a stationary vehicle providing reasonable protection, or the operation meets one of the Subpart D operational categories (§§ 107.100–107.145, covered in ACS Area I, Task E).

• 400 feet AGL is the general altitude limit under § 107.51(b); it has nothing to do with the separate overflight permissions in § 107.39, which turn on the person's location or participation, or on meeting a Subpart D category.
• Part 107 does not require any advance-notice period before overflying a non-participating person; § 107.39 conditions the overflight on the person's location or participation, not on notice given beforehand.