E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
The spear of the the angel Ithuriel, the slightest touch of which exposed deceit. Hence, when Satan squatted like a toad close to the ear of Eve, Ithuriel only touched the creature with his spear, and it resumed the form of Satan.
Him [i.e. Satan], thus intent Ithuriel with his spear