Nit: Harry correctly guessing before this chapter that the resonance affects mainly the caster in proportion to the caster's strength seems overly specific. His experience did indicate that the resonance was a greater threat to V than to himself, so his actions were justified, but his prediction should have been more disjunctive: Either the resonance mainly affects the caster in proportion to the caster's strength, or it affects both parties in proportion to their strength, or it mainly affects V regardless of who casts what due to some asymmetry, or it affects the caster in proportion to the spell's magical strength, or something else.