my garter snakes feces often looks red, is it blood or could it be pigment from the scales of the fish he eats?

this time it looked runny, there was alittle bit of red stuff and alittle bit of "pus" looking liquid. but other times the feces is normal shaped but looks alittle red.

could it be blood from a cut in his asophogus? an ulcer?

should i stop feeding him for a couple weeks or feed smaller meals?
-----
Jake Barney

snakes
2.2. ball pythons
0.2 corns
1.0 bcc
0.0.1 garter
0.0.1 baby snapping turtle