Sforno on Exodus 8:11/ספורנו על שמות ח׳:י״א

1כי היתה הרוחה, even though the evil had not been removed totally, seeing that the stench of the dead beasts remained and putrefied the atmosphere, and these beasts remained in the river as a possible threat in the future.

2והכבד את לבו, He reinforced his natural courage not to be frightened of a re-emergence of the crocodiles that had remained alive. He was also willing to put up with the stench of the decaying beasts. All of this rather than to admit his impotence vis-à-vis the G’d of the Israelites.