To anyone who is not a twin, twins are fascinating. They have a lifelong bond that other siblings may envy but cannot hope to emulate: they share their own language, plot their own games from early childhood, share bedrooms and birthday parties.
For Leanne Houghton, 15, that special closeness was to save her life.
It is not unusual to hear of one twin getting a headache when the other has a migraine, or feeling a twinge in a tooth when the other has a filling. But when Leanne, who is epileptic, had spent too long in the bath, it was her twin Gemma's "sixth sense" that drove her to burst into the bathroom to find her sister unconscious in the water.
Gemma dragged Leanne out and, using her first-aid skills, managed to revive her.
According to newspaper reports, Gemma always feels dizzy when Leanne has a fit.