"In this case, the prosecution say a knife was used to force the girls to hand over the mobile phones. If you are not sure about this issue, the use of the knife, then you must acquit the defendant; the element of a threat of force is not proved. If you are sure, ladies and gentleman, that a knife was used and that the defendant knew that to be the case, go on to consider whether the defendant played any part or not in this offence of robbery."