Possible Clues:

• Pedicure target
• Area of hard skin
• A foot problem? We'd like to hear from you
• It's a bit thick to phone to us like this
• Bit of a thick skin that's required to contact the Guardian?
• It's a bit thick to wake us up like that
• Corn
• Result of being rubbed the wrong way?
• Ring America if you have a skin problem
• It's a bit thick the way they keep phoning here