A Chihuahua wearing a Mexican-themed festive costume with mock guitar after the Chihuahua races held for the Si Se Puede Foundation's Cinco de Mayo Festival in Chandler, Ariz. on May 3, 2014.

Chihuahua dog owners release their pets to compete in the "Run of the Chihuahuas" annual race in Washington on May 3, 2014.

A Chihuahua wearing a jockey rider costume harness looks on before running down a stretch of grass during the Chihuahua races held for the Si Se Puede Foundation's Cinco de Mayo Festival in Chandler, Ariz. on May 3, 2014.

Chihuahua Cooper Babb is dressed in a costume at the 7th annual Running of the Chihuahuas event on May 3, 2014, at the First Tennessee Pavilion in Chattanooga, Tenn.

A chihuahua named Benito wears a Mexican sombrero during the Chihuahua races held for the Si Se Puede Foundation's Cinco de Mayo Festival in Chandler, Ariz. on May 3, 2014.

A chihuahua receives encouragement from its owner to run down a stretch of grass during the Chihuahua races held for the Si Se Puede Foundation's Cinco de Mayo Festival in Chandler, Ariz. on May 3, 2014.

A Chihuahua named Diablo wears a Mexican sombrero during the Chihuahua races held for the Si Se Puede Foundation's Cinco de Mayo Festival in Chandler, Ariz. on May 3, 2014.

A Chihuahua struts in a Mexican-themed festive outfit after the Chihuahua races held for the Si Se Puede Foundation's Cinco de Mayo Festival in Chandler, Ariz. on May 3, 2014.

Chihuahuas compete against each other down a stretch of grass to their owners during the Chihuahua races held for the Si Se Puede Foundation's Cinco de Mayo Festival in Chandler, Ariz. on May 3, 2014.