Possible Clues:

• Not be a good confidant
• Flap one's gums, that's slang for 'talk incessantly'
• Chatter indiscreetly
• Talk, talk, talk
• Yak and yak
• Spill, as a secret
• Lack discretion, in a way
• Spill something in key test area
• Tell on
• Spill secrets of British research facility