Lump with blood and puss on two day old chick
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I think that's the chick version of the umbilical cord stump, from where the chick ingested the last of the yolk and veins, it should dry up and heal by itself. I've had it with 2 chicks and it cleared up by the end of the week.
ooh probably best to keep it separate until it heals to prevent infection if they are pecking it.