It is widely thought that you can’t see what is going on with your shot without a naked/bottomless portafilter, but this isn’t entirely true
In this clip you can see surging in the flow of the mouse tails – this indicates that my distribution & tamping of this shot has been less than perfect and as a result there is some channelling in operation
If there is no channelling the mouse tails will run smoothly until you hit blonding, when they will quaver, giving you a signal to pull the cup