A metal comb with fine teeth on one side and coarser teeth on the other, originally designed for Greyhound coats but now universal in professional grooming. Used to verify brushing reached the skin and to locate hidden tangles.
The single most important tool for confirming thorough grooming. If a greyhound comb snags anywhere, brushing isn't complete.
Always comb after slicker brushing. Start with the coarse side to find tangles, finish with the fine side to confirm smoothness to the skin.