Possible Clues:

• Challenge as questionable
• Dispute the honesty of (motive)
• Challenge in a way
• Cast doubt on
• Dispute the honesty (of a motive)
• Assail with arguments
• Setter's a dog - no! Challenge as false
• Challenge one heartless man confining a dog
• Challenge Inspector Morse's procedures, usually getting nowhere at first glance
• Attack verbally