What does Atticus tell scout about why the jury took so long to convict Tom?

Atticus' discussion about the jury is with Jem.

“Tom’s jury sho‘ made up its mind in a hurry,” Jem muttered. Atticus’s fingers went to his watchpocket. “No it didn’t,” he said, more to himself than to us. “That was the one thing that made me think, well, this may be the shadow of a beginning. That jury took a few hours. An inevitable verdict, maybe, but usually it takes ‘em just a few minutes. This time—” he broke off and looked at us. “You might like to know that there was one fellow who took considerable wearing down—in the beginning he was rarin’ for an outright acquittal.”

“Tom’s jury sho‘ made up its mind in a hurry,” Jem muttered. Atticus’s fingers went to his watchpocket. “No it didn’t,” he said, more to himself than to us. “That was the one thing that made me think, well, this may be the shadow of a beginning. That jury took a few hours. An inevitable verdict, maybe, but usually it takes ‘em just a few minutes. This time—” he broke off and looked at us. “You might like to know that there was one fellow who took considerable wearing down—in the beginning he was rarin’ for an outright acquittal.”