There are only two reasons to see The Heat. But they are formidable reasons, and they go by the names of Sandra Bullock and Melissa McCarthy. They play cops. Bullock is Sarah Ashburn, a socially inept FBI ramrod with her eye on a bigger job. McCarthy is Shannon Mullins, a battering ram of ball-busting fire who makes life hell in the Boston PD for anyone who gets in her way. Of course, Sarah sticks in her craw. Of course, the two will eventually bond. Of course, Bridesmaids director Paul Feig will put a shine on every cliché in the R-rated cop comedy book. The subtext in the all-over-the-place script by Katie Dippold is that women can behave just as boorishly as guys. Point taken, but that point gets tired very quickly. What does work is the hilarious interplay between the two stars. Learning that the irritating Sarah was once married, Shannon deadpans, “Was he a hearing man?” McCarthy is a force of comic nature. And she and Bullock mix it up like pros. In this dead-battery of a movie, these live-wires miraculously ignite sparks.