Electrical components that modify current
Current is the flow of charge. If current flows in, but doesn't flow out, then charge must be accumulating. An example of such a phenomenon would be a gold-leaf electroscope. 

In electronics we usually don't consider that effect or model it with lumped parts like parasitic capacitors to ground, so the current into the electroscope is matched by a hidden ground current. 

Since Q = C\$\cdot\$V, for very small (parasitic) capacitances, significant charge means enormous voltages.