What does Alex think to himself when the police give him a statement to sign? Why?

At first, Alex puts up a fight, but when he is beaten badly, Alex suddenly becomes very agreeable and ceases to insult or resist the police officers. When P.R. Deltoid spits in his face, Alex says thank you. This is strange, and unlike how we have seen Alex thus far in the novel. Soon afterwards, though, Alex realizes that being nice won't get him anywhere and he reverts to his defiant self.