DD did this, we were living in Oman and she and her friend were mooching around the garden in the nude, matey boy dropped a couple of balls out and DD picked one up, looked at it and stuck it in her gob. Initially me and boy's mum were laughing at the sight of him crouching and grunting, laughter turned to nausea when girl performed. She wasn't hurt by the experience and still has a strong bond with boy.