Possible Clues:

• Five-foot line
• Verse form favoured by Shakespeare
• Quietly come on stage, retaining dull line of verse
• Line of five metric feet
• 'Shut up about domesticated queen', for instance
• Write poor letter, losing half - Friar Laurence's usual line
• Write dull words when tossing off manuscript verse
• Draw out new tape measure, it's five foot long
• Domesticated seabird briefly appearing by writer's feet?
• Typical Shakespearean line