What the heck is this stuff

This yellowish phlegm-like substance has been only his urates for a good two months now, since just after christmas. It doesn't look like liquid urine to me, honestly. I'm wondering if it's due to the diet change from mice to strictly rats, or if its a delayed reaction from some of the shots(injected amakacin, which is supposed to be hard on the kidneys) I gave him for a minor RI back in November. My vet said it was nothing to worry about on his last checkup, but it's just disturbing to look at for some reason.

Is this something someone could identify for me?

http://i39.tinypic.com/2e5l0r4.jpg
http://i39.tinypic.com/2e5l0r4.jpg

I only cant tell you what it is but im pretty sure ive seen it from one of my bps before so i wouldnt really worry.

Not sure the proper name for it but it looks perfectly normal to me. No worries.

Ok, so long as it's normal I won't be concerned. My vet never said anything specific, and it seemed to come out of nowhere with no significant change to the diet(mice and rats aren't that different).

Anyway, I appreciate this. I want to make absolutely sure there are no irregularities in his health, no matter how minuscule the detail may be.