You propably connected only one particular mole from the starting scene to the listener.
It is better to disconnect it there, and code it in mole script :
onready var listener = #reference to your listener here
connect( "whack", listener, "on_whack")
first argument is signal name, 2nd is node to listen, 3rd is a name of function in listener that will trigger. You can also add 4th argument and more, they will be passed as additional information. For example You can pass reference to a mole being hit by entering
self as 4th argument. The same can be done when emitting signal :