"My card?" She responds, initially puzzled. But then it clicks. "Oh, right."

She scrambles for her bag, and hastily pulls out her plastic UCL student card. It's quite plain, with her photo and student number on it. Hastily, she flips it over and with a Sharpie, scribbles her mobile number above the barcode on the back.
"Here," she says, handing it over. "Sorry it's a bit scratched. I dropped it in the gym the other day."