Sometimes, squirrel cage induction motors exhibits a tendency to run at very slow speeds (as low as one-seventh of their synchronous speed). This phenomenon is called as crawling of an induction motor.
When the rotor teeth and stator teeth face each other, the reluctance of the magnetic path is minimum, that is why the rotor tends to remain fixed. This phenomenon is called cogging or magnetic locking of induction motor.
Cogging means magnectic locking, when the speed of the stator flux is equal to rotor flux that time it will happen due to improper design of rotor.
When motor runs at one seventh of the rated speed is known as crawling.