Friggatriskaidekaphobia

The fear of Friday the 13th has been called friggatriskaidekaphobia (Frigga being the name of the Norse goddess for whom "Friday" is named and triskaidekaphobia meaning fear of the number thirteen) -Wikipedia

Tyson looked at calendar in Dinning Pavilion with fear.

"What's wrong? What is the matter? What seems to be the problem?" Ella asked him, hopping on the floor next to him.

"Friday the 13th," he said. "Uh oh. Bad."

"Why?" Ella asked.

"Unlucky day is bad." Tyson said.

"Not unlucky." Ella said. "Unluckiness is just superstition. Opposition to superstition was a central concern of the intellectuals during the 18th century Age of Enlightenment."

"Not superstition, the gods will it." Tyson said nodding.

"Wikipedia the free encyclopaedia: In Italian popular culture, Friday the 17th (and not the 13th) is considered a day of bad luck. In fact, in Italy, 13 is generally considered a lucky-"

"Not Italian," Tyson reminded her. "Friday the 13th no good for Tyson."

"'A fool's brain digests philosophy into folly, science into superstition, and art into pedantry. Hence University education.' George Bernard Shaw." The harpy quotes.

"Ella calling Tyson a fool," Tyson said suddenly, as if the meaning of life was dawning on him.

"No!" Ella said. "Ella not calling Tyson a fool. I have much to say why my reputation should be rescued from the load of false accusation and calumny which has been heaped upon it. –Robert Emmet."

"So now Ella's calling Tyson a liar," he said.

"No, no, no!" Ella said. "Non. Nai. Never!"

"Never? But right now? Ella thinks Ella is so much smarter than everyone. Like a diva." Tyson said.

"Apologise!" Ella chirped, offended.

"Tyson doesn't need to apologise!"

"Ella not calls Tyson a fool or a liar," Ella said. "But now Ella calls Tyson a meanie!"

And with that she hopped out of the dining pavilion, like a robin, leaving Tyson standing alone and the dining half-bloods wondering what the hell they'd just seen.

Tyson went into the stables and sat down on the little attic over it, where Ella was huddled with books that had been donated by the Athena cabin after Annabeth had promised that Ella took care of books better than a museum curator would.

"Tyson is sorry," he said. "Tyson didn't mean to make Ella sad. At all. Tyson always wants Ella to be happy. And Ella was right. Friday the 13th is bogus."

Tyson had checked with Annabeth, who was the highest authority aside from Ella as far as brains were concerned.

Ella looked down at her books, sadly, and drew her nest closer to herself.

"Tyson apologises? Ella thought that Tyson didn't want to apologise. Ella thought that Tyson thought he was right."

"Even if Tyson was right," the Cyclops said, "Tyson is more scared of losing Ella than of any day of the year."