Regurgitation?

[Albert Clark]

I wonder if they could test that "pink spot" first, to see if it's actually blood? (I'm not sure if it's "enough" of a sample, but there are ways to test for the presence of blood.)

I believe there is a reagent liquid that they use similar to a guiac test in humans for the presence of blood. The guiac test does require a stool sample in humans. Testing paper towel is probably done microscopically.