his/her mistake
Tom a essayé de dissimuler son erreur.
Tom tried to cover up his mistake.
À mon avis, c'était son erreur.
In my opinion, it was his mistake.
Tu ne devrais pas te moquer de son erreur.
You shouldn't make fun of his mistake.
His mistake was costly.
Il vient de comprendre son erreur.
He has just realized his mistake.
Ne vous moquez pas de son erreur.
Don't make fun of his mistake.
Je ne pus le convaincre de son erreur.
I could not convince him of his mistake.
Ils rirent tous de son erreur.
They all laughed at his mistake.