What was Tom doing when Ben was whitewashing the fence?

While Ben was whitewashing the fence, Tom was relaxing, eating, and planning how to fool more kids.
In chapter 2, Tom is whitewashing the fence, and he is not enjoying it; however, Tom isn't about to let Ben know that. Ben shows up at the fence planning on teasing Tom about having to do work while he plans on having fun.

"Say—I’m going in a swimming, I am. Don’t you wish you could? But of course you’d druther work—wouldn’t you? Course you would!"

Tom, being his crafty self, responds by telling Ben that whitewashing the fence could hardly be called work. Tom then proceeds to act like he is working on a great piece of art. He paints a little, then critiques it, then adds a little touch of paint here and there.

Tom swept his brush daintily back and forth—stepped back to note the effect—added a touch here and there—criticised the effect again—Ben watching every move and getting more and more interested, more and more absorbed.

Tom claims that it's not work because it's something that he doesn't get to do all that often. All of this subtle enticement convinces Ben that he wants to paint the fence, and he begs Tom to let him have a chance. Tom refuses, but then Ben offers to pay Tom for the privilege of whitewashing the fence. Tom "reluctantly" agrees to let Ben work on the fence, and Tom sits on a nearby barrel in the shade while eating an apple and planning to trick more kids.

And while the late steamer Big Missouri worked and sweated in the sun, the retired artist sat on a barrel in the shade close by, dangled his legs, munched his apple, and planned the slaughter of more innocents.