It can be done by asking some obvious question for humans: "This is a anti-robocall system, please answer the question to complete the call. A mother cat and h

It can be done by asking some obvious question for humans: "This is a anti-robocall system, please answer the question to complete the call. A mother cat and her three kittens are sleeping in a box. Dial the number of animals in that box." The number of kittens change randomly and maybe the system can put some pillows, blankets and other non-animals in the box too, making automated processing harder. AI will get there, sure, but this will make things expensive for the attackers.