Huck and Tom finally seem to come to their senses and grow up a little in this scene. Tom realizes and accepts that his plan is impractical, so he resigns himself to pretending, which, as Huck rightly points out, is harmless enough. He and Tom can save Jim in a timely fashion and Tom can have his adventure too. That being said, Tom is still insistent that Huck fetch some knives to dig with, bad tools for the job, impractical, fantastical, and farcical.