I believe that would be the female exhibiting cloacal gaping. From what I understand it usually means that the female is not interested, either because she's not sexually mature yet or she just doesn't like that male.
I have heard some people report just the opposite though. That the female could be spreading pheromones around to entice the male.
Personally I have seen one of my female Nics do this. She's an '05 so I thought she might be ready to breed. Within 5 minutes of the initial introduction of a male Nic, she thrashed her tail, wandered all over the cage until her tail was perched on the rim of the waterdish, and she expelled a lot of liquid and urates. The male was very interested immediately after and chased her around for a few hours. By morning they were on opposite sides of the enclosure. I have not seen any breeding activity from them. I think my girl was telling the male to "back off".
Amie