Niles explains the main points of the myth of Oedipus to Martin: that he sleeps with his mother and kills his father and then gouges out his own eyes. A nod to the eye gouging occurs when Frasier blinds himself with bug spray.
Frasier's mom was first seen in Cheers' Diane Meets Mom (1984), when Fraser and Diane were going to be married. She was played by Nancy Marchand.
Mia is probably the only character in the entire series who has no reaction whatsoever when she first enters Frasier's apartment.