Borders between ecosystems are subtle or imperceptible. State collapse is often a gradual process of slow, imperceptible, generational change. The amount of iridescence may vary from almost imperceptible to very visible. However, the discontinuity is usually so slight as to be imperceptible. The result is that the connection moves instantaneously, with an imperceptible interruption to the conversation. Noise from passing trains is audible within the radio theatre, but generally imperceptible in recordings. It did cause a usually visibly imperceptible loss of quality when doing heavy blending. Some watermarks can be inserted in a way that they are imperceptible by a viewer. They also stated that the gearshifts were so smooth as to be practically imperceptible. It is the "One", "Eternal", and "All Pervading" physical substance, which is imperceptible. The concept of the imperceptible is a decisive factor in distinguishing man from animal. The difference in speed is imperceptible to the viewer. At first Nebel said the motion was almost imperceptible. Ions with low charges, such as Na are very weak acids with almost imperceptible hydrolysis. Actual change, however, was nearly imperceptible.