I believe the answer is: A just-noticeable difference
In painting, A just-noticeable difference refers to the amount of things that needed to be change for a difference to be noticeable.
The threshold usually depended on the type of audience that being aimed toward, (for common audience, the threshold of differences would be relatively higher compared to expert audience)<span />
Populated :/ right? Love ya much Fam ;)
A few months after birth or a year, seeing as twins can get so close within those few months and develop separation anxiety from their twin