On the boat, Rat was taken by surprise and fell backwards when mole ?

From the text:

The Mole was quiet for a minute or two. But he began to feel more and more jealous of Rat, sculling so strongly and so easily along, and his pride began to whisper that he could do it every bit as well. He jumped up and seized the sculls, so suddenly, that the Rat, who was gazing out over the water and saying more poetry-things to himself, was taken by surprise and fell backwards off his seat with his legs in the air for the second time, while the triumphant Mole took his place and grabbed the sculls with entire confidence.