Complex contagion (Watts 2002): unlike disease spread, social adoption requires multiple reinforcing contacts. A node adopts when fraction of neighbors already adopted ≥ threshold φ.
Global cascade condition: exists only when a "vulnerable cluster" of low-φ nodes spans the network. Scale-free networks are surprisingly cascade-resistant — hubs need many neighbors to convert.
Click any node to seed it. Try seeding different nodes and watch how far cascades propagate.