What is three to four miles long, an inch in diameter and five times hotter than the surface of the sun? Anyone in Hong Kong this week is more likely than most to come straight out with the answer, Lightning! (Pearl, 8pm), as we have had more than our fair share this week.
This documentary accompanies intrepid scientists (and one photographer) into the most electrically charged weather in the world to examine one of nature's most dazzling and dangerous displays.
Lightning strikes the Earth 6,000 times a minute, jolts every commercial plane roughly once a year, wipes out power to entire cities, hits 1,000 people annually and, on average, accounts for more deaths than tornadoes and hurricanes put together.
Which all make good reasons for scientists to study - albeit gingerly - these fleeting, sometimes fatal flashes of electricity.
Two centuries ago, Benjamin Frankling performed history's most famous lightning experiment by flying a kite in a storm.
The electrical charge that travelled down the wet string to a dangling key proved that lightning is a form of electricity, not a supernatural force as many believed at the time.