DNS64
A resolver that lies helpfully: when a name has no AAAA record it invents one by embedding the IPv4 address inside an IPv6 prefix.
The technique exists so a client on a pure IPv6 network can reach servers that only have IPv4. When the AAAA query comes back empty the resolver looks up the A record instead and synthesises an answer whose last thirty-two bits are the IPv4 address, usually under the well-known prefix 64:ff9b::/96. The client connects to that address like any other IPv6 destination, and a NAT64 gateway along the path translates it into real IPv4. Two limitations follow: synthesised answers cannot be DNSSEC-validated because the zone never signed them, and applications that pass IPv4 addresses as text inside their own payload get no help whatsoever.