We have two unrelated cats who are a little over three years old, male and
a female.  Ever since they were kittens they have both been obsessed with
this one particular spot in the bathtub.  The spot is about six inches
southwest of the drain.  To us, it doesn't look or feel any different from
any other spot on the bathtub, but they both love it.  They ask to get into
the bathroom, then go jump in the tub and start licking this spot.  They
will usually lick it for about 20 seconds and then leave.

We can't figure it out.  I know cats can get crazy about some kinds of
scouring powder, and one of ours does, when it (the powder) is dry.  But
that doesn't explain this little weirdness.  Because we use scouring powder
on the whole tub, not just this one spot, but they keep going back to it.  
It's not about water, because if they want to drink in the tub (not often),
we run the water and they drink out of the tap or just below it.  The
"spot" doesn't even get wet in these circumstances, so I am sure it is not
about being thirsty.

Any body ever see anything like that?  It is so weird.

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