Some of the factors considered by the Assyrian diviner in identifying and distinguishing one fortuitous mark from another are described in the following passage:
Considerations like these helped the diviner to ascertain, for purposes of prediction, the ominous worth of the numerous configurations and markings which abounded on the surface of the exta.
Of the last four markings mentioned in the passage cited, at least two, larû and uṣurtu, merit some discussion, because they are well-attested in the omen literature and in the reports and queries.
Ivan Starr
Ivan Starr, 'The Identification of Fortuitous Markings', Queries to the Sungod: Divination and Politics in Sargonid Assyria, SAA 4. Original publication: Helsinki, Helsinki University Press, 1990; online contents: SAAo/SAA04 Project, a sub-project of MOCCI, 2020 [http://oracc.org/saao/saa04/OtherPartsandFeaturesoftheExta/TheIdentificationofFortuitousMarkings/]