Cleaning old houses commonly yields strange and surprising things. If a pet had an accident in an inconspicuous area and your last cat died in 1971, the fecal matter's adhesion to the carpet may have strength seemingly comparable to aircraft glue. Fully remove petrified waste from porous fibers, by first softening the bond between the two. Employ a softening agent that will not discolor or mar the finish of the fecal matter's unwitting host.
Wear latex gloves to avoid skin contact with the waste matter. Pick off any loose bits, and scrape or slice off as much excess stuck-on matter as possible, using a metal putty knife or paint scraper. Take care to not cut or fray the fibers.
Vacuum over the area to suck up any bits lost deep in the nap.
Place several folded up paper towels that have been drenched in steaming hot water over the remaining stuck-on feces. Press down on the paper towels to ensure they are making contact with the feces. Leave the moisture and steam coming from the paper towels to soften the dried remnants for several minutes.
Pinch in the center, when removing the paper towels and pull up as much of the softened feces as possible.
Create a cleaning solution of hot water with a drop of dishwashing liquid and a splash of white vinegar. Bolt the area repeatedly with the solution then gently brush the final vestiges of waste with a mini scrub brush or an old toothbrush.
Vacuum the area once more, to remove the last of the fecal crumbs. Blot the area with a sponge and clean water to remove residue left from the soap solution.