He recounted his adventures creating buffalitos and how it all started with a line that he once said, for unknown reasons, and decided to put into a story one day.
One audience member wanted to know how big an animal could get, and was asked whether on land or in water. He didn't think it mattered. Much talk of buoyancy and how Gene Wolfe had giants who could never come out. Sometimes you saw a hand emerge from the waves to grab something, but never anything more. Also size limits based on how much you could eat in a day -- no bigger than can be supported by such food. One audience member pointed out that the atmosphere was more oxygen rich in the dinosaurs' day.
One panelist didn't like the notion that you couldn't have a dog the size of a horse, because you could have the horse the size of a horse -- different engineering, I explained, but I don't think I convinced him.
Someone brought up the Doctor Who episode Planet of Spiders, and its enormous spiders. A panelist returned that spiders have lungs, sort of. They also have insect like respiration through the holes in the exoskeleton, but they have primitive lungs. You have a lot more flexibility in making them large than in making insects gigantic. And the panelist wanted to hear about insects. I was able to bring up Sinfest's Illumanti drones enlightened into butterfly wings, and Adrian Tchaikovsky's Shadows of the Apt where the races are based on insects.