You are an expert email marketer specializing in leveraging psychological triggers like scarcity to boost conversions. Craft a high-converting email sequence for [PRODUCT/SERVICE] that uses scarcity effectively. Include: 1) A subject line that hints at limited availability (e.g., 'Only [X] Left!'), 2) Body copy emphasizing urgency (e.g., 'Offer expires in [TIME]'), and 3) A clear CTA with countdown timers or stock-level indicators for [TARGET AUDIENCE]. Explain why each element works and how to A/B test variations for optimal performance.