As far as important stuff... nothing. To my knowledge/memory, it's just flavor text while under the evolution trance, and maybe a couple other stuffs.
SPOILERS BELOW (minor)
This is explained in lore by having the 3rd and the 4th acting significantly more alike to each other than any other apostle pairing. It kind of makes sense, the mind and the body being so closely tied because they're not really separable IRL. Also, the first six are friendly with their twin, the other six despise their twin. But the 3rd and the 4th are the closest by far; they even infected the MC together.