After an “r”, and before a spirant followed by a vowel, there is an insertion of a vocalic fraction, which is [equivalent to] half of a short “a”, or quarter according to some [authorities]. [After “r”,] before another consonant [= non-spirant], [the inserted fractional vowel is equivalent to] a quarter or an eighth [of a short “a” in duration]. That is itself [called] “sphoṭana”. (pp. 255-257)
- Deshpande (1997), Pag.

[In a stop+stop combination], in the reverse order of the stop-series [i. e. reverse of the normal order: “k”-series, “c”-series, “ṭ”-series, “t”-series, and the “p”-series], there is an insertion of a “sphoṭana” [i. e. a vocalic particle of one-eighth mora length, between the stops], if the first [stop of the combination] occurs at the end [of a “pada”]. (p. 301)
- Deshpande (1997), Pag.