Mysterious white plug in rat pee?

Question
I have two little ratty boys.  About a month ago, I noticed
one of the boys was working on something in his private
area.  I came over to him just in time to see him pull
something white out of his little wee wee and eat it.  
After I squealed to my boyfriend in disgust and worry, my
boyfriend convinced me that he must have been just being a
guy, handling his own business so to speak and that I
should leave him be.
Well today, the same little guy was sitting with me on the
couch being scritched happily.  When he hopped off my lap
there was a little pee dribble (normal) and a white rubbery
looking pellet that looked EXACTLY like what he had eaten a
month before.  I have this thing (saving it to bring to the
vet).  It is milky-white, rubbery and solid.  
What is this?  Is this normal or does this point to kidney
problems?  Neither of the boys have shown any other signs
of poor health.  They run and play just as much as ever,
water intake has not increased, and he's not losing weight
(if anything he's a bit on the pudgy size... 30 grams
fatter than his svelte brother on the same diet).  Any clue
as to what this is?

Answer
It may be a bit of seminal fluid that has dried up inside his penis.  If he doesn't appear to be in pain, is still able to urinate, and isn't showing any other symptoms of illness it is probably fine, just keep an eye on him to make sure.  Good luck with your rats!