Twins

Francis Kynaston (1587-1642), "To Cynthia: On a Mistress for his Rivals," lines 53-56:

Her cheeks and buttocks shall so near agree
In shape and semblance, they shall seem to be
Twins by their likeness, nor shall it be eath
To know, which is which by their fulsome breath.

eath: easy
fulsome: foul-smelling, stinking (Oxford English Dictionary, sense 4.b)