Taylor Swift says she got with Calvin Harris because of this tweet from Lady Gaga.

Huh. Seems like general well-wishes, but not according to Tay-Tay:

I guess well-wishes could be a "spell," kind of. Like saying "gesundheit" might cause a sneezing person to have good health forever after. And if there's a pop singer who I think might actually have some connection to the dark arts, it's Lady Gaga. You definitely need black magic to get through the night wearing a meat dress.

Sources: Taylor Swift | Lady Gaga