Ice Rule: Each tetrahedron obeys "2-in, 2-out". Violations create emergent monopoles (+3-in or 3-out) carrying magnetic charge Q=±2μ/a². They are connected by Dirac strings — chains of reversed spins.
Key: Monopoles interact via Coulomb law V(r)=μ₀Q²/4πr, effectively free charges despite no fundamental monopoles.