This has happened to me a couple of times now so I thought it was worth sharing.
While cleaning a repeat customer’s apartment building in a senior center for a move out, I came across what looked like a normal spot/stain. I presprayed the dark brown substance with Revive iT hydrogen peroxide stain remover and vacuumed the apartment. After I cleaned the apartment I noticed that the discolored area had not become completely clean. I thought “did my chemical fail me?” I re-sprayed the spot and still not much improvement. I switched to Surround and repeated but this time I got a very absorbent commercial cleaning paper towel and folded it several times over and placed it on the spot and stood on it for about 10 seconds. When I removed my foot I was surprised to see how filthy it was. I repeated this two more times with a total of 21 layers of folded cloth to remove this very concentrated material from the carpet.
Just a little trick I use for the really concentrated spills when extraction is not available.
by John H. Klucznik, Founder of Bonnet Pro and Key Floor Care