All piggul [foods] combine with one another. All nossar [foods] combine with one another. All neveilos combine with one another. All shera- tzim combine with one another. The blood of a sheretz and its meat combine with each other.  R’ Yehoshua stated a general rule: All [items] whose tumah [transmission] and [minimum] measure are the same, combine with one another. [If] their tumah [transmission is the same] but not their [minimum] measure, [or if] their [minimum] measure [is the same] but not their tumah [transmission], [or if] neither their tumah [transmission] nor their [minimum] measure [are the same], they do not combine with one another.