What is the effect of the double jeopardy rule on a jury trial?

The rule that jeopardy attaches when the jury is sworn or the court as trier of fact begins to hear evidence, is "by no means a mere technicality, nor is it a 'rigid, mechanical' rule. It is of course, like most legal rules, an attempt to impart content to an abstraction." (Serfass v. United States (1975) 420 U.S. 377, 391, 95 S.Ct. 1055, 1064, 43 L.Ed.2d 265.) I would adhere to the rule to preserve the content of the double jeopardy clause.