Rashi on Exodus 7:11/רש"י על שמות ז׳:י״א

1בלהטיהם The Targum renders this by בלחשיהון: with their secret spells. There is no other example of this word in the Bible. One may compare it to the first word in (Genesis 3:24) “the להט of the sword that turned round” — it appeared to turn round through some magic spell.