Suck eggs

The Adventures of Tom Sawyer, chapter 1: Tom is arguing with a stranger and one of them said "I dare you to knock it off-and anybody that'll take a dare will suck eggs." Does anyone know what is meant by the slang "suck eggs"?

Haven't you ever sucked an egg? SS

And another thing -- an "egg-sucking dog" was a very bad thing to have on a farm.