Chanita asked about puppies/kittens etc. having a nipple preference.  I
don't know.  But we had Peter Hartmann here a couple of years ago.  He has
done extensive research for the pig industry, and I think I remember him
saying that piglets each have their "own" teat.  I gave my twin boys their
own breast at 10 months, after the smaller one went on a strike and I gave
him his favourite breast to coax him back.  Now I have one left-handed and
one right-handed twin (and no, they're not mirror-image twins, we had them
tested at 4 years of age, they both had right-foot dominance, right-eye
dominance, but different hand-dominance so I think it's environmental, not
congenital).

Pamela, Zimbabwe