They probably had many mock executions prior to this one. After a while, you don’t know when the actual execution will take place.
>From what I have read in the Brit papers that is exactly what happen to Foley.
They believe the video of Foley was not the actual beheading.
That was done at a later date, with the final video of his head place on his back being the final shot/
Heritage on Fox said that Sotlogg beheading was done some time later judging by his beard and the growth of his hair.