Parshas Bo
In the possuk when Moshe came to Pharaoh to tell him about the plague of Arbe [locusts], it says he turned and left. What was different about this plague that it specifically says he left?
Ramban--- explains that this was true by all the plagues. Moshe would tell Pharaoh about the plague and leave. To shorten the text, the posuk only says it the one time.
Rabeinu Bachayaa—says that this was only true for this plague. He explains by the previous plague of hail, Pharaoh had realized for the first time they were all going to die since the hail was ruining all the crops. Now that locusts were coming, Moshe wanted the wise men to convince Pharaoh that they would be totally finished if they don’t give in, since there would be no more food at all. Moshe quickly left, before Pharaoh could answer that he would not let them go, to give them a chance to mull it over.