Happy Jack in "Happy Jack Has A Happy Thought"

But when that scent led him out on a branch the tip of which brushed against Farmer Brown's house Shadow got another surprise. There was no sign of Happy Jack. He couldn't have reached the roof. There was no place he could have gone unless—. Shadow stared across at a window open about two inches.
"He couldn't have!" muttered Shadow.
"He wouldn't dare. He couldn't have!"
But Happy Jack had. He had gone inside that window.