Many studies revealed that parasitic young mostly emit signals that are used in parent-offspring communication of hosts, but sometimes not. The terms used to explain host manipulation signals are not unified, then presenting confusion. Here we propose a new categorization of signals used for parasitic manipulation. Host manipulative signals could roughly be divided into two patterns according whether a parasite exploits signals actually used in parent-offspring communication of hosts (signal exploitation) or not (sensory exploitation), in relation to particular selective pressures that parasites face, such as nestling discrimination by hosts or deficient stimulation by parasites to obtain sufficient food.