Possible Clues:

• It's a bit thick to wake us up like this
• It's a bit thick to get us up like this
• "We want to hear from you"
• Let the Guardian know about thickening skin?
• A thick-skinned generation: unfeeling, old, ignored
• Hardened tissue
• Feature of a guitarist's finger
• Bit of a thick skin that's required to contact the Guardian?
• Left student absorbed by reason mainly for a thickening of tissue
• Area of skin hardened by friction