Clue: Heaven observed: head turns when this happens, by the sound of it? (4,5)
Answer: NEXT WORLD
Explanation: Definition: Heaven
definition: 'next world' refers to a life after death 
sounds like/"by the sound of it": 'Neck's twirled'="head turns when this happens"
 
is "observed" there to justify the past tense in 'twirled'?