Related Clues:

• Think tank output
• 'Gibraltar may be strong, but ___ are impregnable': Emerson
• Concepts
• Brain waves
• They're sometimes funny
• Lightbulbs, in the comics
• Themes
• Bright thoughts
• Cortex activity
• Gray matter output
• Lamb products
• Bean products?
• Written themes
• Suggestion box fill
• Puts to the test