Possible Clues:

• Pet can be taken in the arms
• Rodent often kept as pet
• Writing concealed by heart-rending creature in a cage
• Short-tailed burrowing rodent
• Henry wants port, but mother's denied the little beast
• Pouch-cheeked critter
• Habitrail walker
• Animal by River Thames, swimming
• Henry wants port but mother's denied the little beast
• Oddly, the arms of a rodent