Complex sentence: Floating in the clouds, he sees the Road Runner and releases the anvil, causing the balloon to rise in the air until it stops and the string keeping it blown up unfurls, sending it flying through the air until it runs out of air.
Split into simpler sentences: Floating in the clouds, he sees the Road Runner and releases the anvil, causing the balloon to rise in the air until it stops. At this point, the string keeping it blown up unfurls, sending it flying through the air until it runs out of air.