Xeph are quick.

Prerequisites: Xeph, Dexterity 23+

Benefit: Once per encounter as a swift action, you can expend two of your daily uses of burst granted by your xeph heritage to gain one extra attack for 1 round, instead of gaining an increase to your speed. While enjoying your round of celerity, you make one extra attack each round, using your highest base attack bonus, when you take a full-attack action.