What theories are given about the scarlet letter imprinted in the minister’s flesh? In chapter 24.

Some speculated it was just a birthmark,

"It is singular, nevertheless, that certain persons, who were spectators of the whole scene, and professed never once to have removed their eyes from the Reverend Mr. Dimmesdale, denied that there was any mark whatever on his breast, more than on a new-born infant’s."