When a Redstone torch is placed onto the side of an opaque block with Redstone dust on it and another is placed on top of the torch it causes a pulse, but when blocks around and below the torch a placed or destroyed it causes the torch to do another pulse after the pulse has finished (usually lasts around a second) there is what seems to be a cooldown period (also around a second long) before another pulse can happen from placing a block. but where the Redstone torch is a source the Redstone dust that was placed on the block the Redstone torch is on seems to make other Redstone dust surrounding it becomes an activator of the pulse even if there is no connection between them which I demonstrated in the video attached. The blue wool blocks create a pulse when Redstone dust on it is placed or destroy after the cool-down period from the last pulse, red wool has the same effect as blue wool but when red wool is broken or placed its starts a pulse. (This happens with other blocks not just wool)