«اِلْكِدْبْ مَالُوشْ رِجْلِينْ»

The image treats a lie as something that needs to travel in order to survive, yet it has no legs to move on. Whatever ground it seems to gain is short, because it is found out before it can get far.

Once discovered, the falsehood loses its force. People stop paying it any heed, and it is left stranded, much like someone unable to rise and walk, going nowhere and carrying no weight.

Fits when describing a falsehood as short-lived: deceit will not hold up for long, will be found out soon, and afterward will count for nothing. A similar 'no legs' saying about a thief means he cannot stand still and flees; that sense does not apply here.