How does Boxer try to use his reason when Squealer says there is 'proof' that snowball was Jones's agent?

when squealer says that snowball was Jone's agent, boxer tries to think, but was vaguely troubled. he set his ears back, shook his forelock several times, and tried hard to marshal his thoughts. but in the end he couldn't think of anything to say. four pigs in the back stood up and was going to oppose the statement but suddenly the dogs let out menacing growls and the pigs fell silent and sat down again.