Highlight from frame 1 to frame 31 in the LASER LINE layer
Right click the highlighted frames and choose 'Insert Blank Keyframes'
Go back to frame 1 in this layer and select the line tool from your toolbox, width of 1 and and dark red color
Make sure the 'snap' feature is turned on and draw a line from the centre of the "ball" symbol in the top
half of the stage to the "ball" symbol that runs along the middle of the stage
Draw another line in the second frame just like in the first frame and continue doing this until all 31 frames have a line
There you have it, a cool effect that once learnt can be done in no time.