Related Clues:

• Slipper without a back
• Plow pullers
• See 26-Across
• Beast of burden
• Part of a wagon train
• Pack animal
• Stubborn beasts
• Beasts of burden
• Symbols of stubbornness
• One who won't budge
• Stubborn sort
• Plodding sort
• Plow puller
• Paid smuggler
• Obstinate ones