at high frequencies, the leads of the components exbit inductance. For the logic gates, if the transition are fast, so beacuse of inducatnce there will be drop across this which inturn will change according to switching.
In effect, the drop across the inductance which is in between chip ground pin and actual pcb ground changes causing the reference of th chip changing dynamically.
some times, because of this inductance there will be ringing ( unnecessary oscillations ) in the circuit......