The video to the left is an example of a masking effect used on Premiere Pro. This effect allows there to be a combination of two clips playing at exactly the same time without any obvious split appearing on the screen. 

Once we filmed the two individual clips and imported them onto the working area on Premiere Pro, we found the 'linear wipe' effect which is found in the video effects and transitions option on the programme. We then applied this effect so that a  black square was present on the left hand side of the screen. However, to get both clips playing together we had to adjust the percentage on the 'transition completion' setting in order for the clip that was playing over the top of the origional would not appear with an obvious split separating the two clips.