At the beginning of your test, the examiner will ask you two 'vehicle safety questions'. These are otherwise known as 'Show me, Tell me' questions. You are asked one of each - so if it's a 'show me', you have to actually demonstrate how to do whatever he has asked. The 'tell me' question is just that - explain the answer, no need to actually do it. You can't fail your test for not knowing the answers, as incorrect answers are counted as 'minors' (driver faults). Unless, that is, your test goes badly wrong and you clock up 14 driver faults on the drive - in which case those 2 extra faults will mean, well you know...the F word.