What is the joke explained by experts?

There were two turtles standing motionless by the field, when an expert asked the old farmer next to them, what are these two turtles doing? The old farmer said, "They are comparing endurance. Whoever moves first loses. " The expert pointed to a turtle with Oracle Bone Inscriptions on its shell and said, "According to my years of research, this turtle has been dead for more than 5,000 years." At this time, another turtle poked its head out and said, "What a fool! I didn't say anything when I died, so let me wait here. " Just after this sentence was finished, only the tortoise with Oracle Bone Inscriptions pattern laughed and poked its head out and said, "You lost, and you believe what the experts said!"