How does Cisco ACI detect the IP address of a silent host that moved from one location to another without notifying a Cisco ACI leaf?

While silent hosts are eventually detected by the ACI fabric, this statement is too general and doesn't explain how they are detected.

Endpoint announce messages are sent to COOP (Council of Oracles Protocol) for known endpoints or those sending gratuitous ARPs, not typically for silent hosts initially.

A silent host is one that moves from one port or leaf to another without sending any Layer 2 or Layer 3 notification (like gratuitous ARP). When the ACI fabric needs to send traffic to such a host but cannot locate it at its last known location, it sends an Address Resolution Protocol (ARP) request for the host's IP address and floods this ARP request throughout the bridge domain. The host will then respond with its current MAC and IP, allowing the ACI fabric to update its endpoint table with the new location.

Bounce entries are created after a move is detected (e.g., if an endpoint is seen on a new port), indicating a change, but they are not the mechanism for detecting a truly silent host initially.