Lance saw Venus crawl to Amelia's side and use his own body to shield Amelia from the Power of Thunder, which made him feel like laughing.
Thunder Tempering must be painful, an unavoidable aspect that lets their bodies remember the process of Thunder Tempering. Once they endure the tribulation, recognizing the benefits of Thunder Tempering, the next time they encounter a thunderstorm and wish to attract thunder for tempering...
Their bodies, bearing the memory of being struck by lightning, will subconsciously use the incoming Power of Thunder to refine their organs and viscera.
He wasn't simply striking them with thunder; once inside their bodies, the trajectory of the thunder from start to finish would quickly dispel the impurities within.
