Whether she's aware of it or not, the pitch of a woman's voice increases a notch (becoming higher but not shrill) when she's flirting, finds a study from McMaster University in Canada. Conveniently, men much prefer these high-pitched dulcet tones over deeper ones. A woman can strike her highest chords around ovulation, when she's likeliest to conceive. Another coincidence: This happens to be the time of the month that men give female voices the highest attractiveness ratings.
Next: Dr. Laura Berman's 5 elements of attractiveness