I'm going with Assassin's Asshilles' (Achilles') heel until someone comes up with something wittier.
*Tap*So it's not a blind spot eh...Eh? What?Assassin's Asschilles' heelEek?!*Smirk**Dash**Flinch**Stare*Doesn't seem like she could see well from this sideHoo...What?!That's the 'Assassin's Asschilles' heel' eh?