There have been several posts recently about these.  I'm a little behind
on reading, so sorry if someone has already mentioned this.  I haven't
seen reference to what makes them unique.  One side (from tip to base)
has a firmer texture/consistency that the other.  I believe the idea is
to have the firmer side against the palate so the baby "milks" the
softer side.  You can't see the difference by just looking at it.
Winnie

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