I argue that there exists a class of phonological phenomenon that, while naturally expressed in parallel OT, remain recalcitrant in the serial instantiation of OT, Harmonic Serialism. The primary case study comes from Mohawk. In Mohawk, the typical foot is a disyllabic, monosyllable. Wherever the canonical stress position, the penult, is open, vowel lengthening occurs to supply the second mora. However, when a separate constraint against long epenthetic vowels blocks lengthening, a disyllabic foot emerges instead. This conspiracy on Mohawk foot structure cannot be derived in Harmonic Serialism, because the constraint driving the conspiracy, FootBinarity, must be demoted, in the course of the derivation. I show that Mohawk is not an isolated case. Rather, the finer detail of Mohawk phonology can be abstracted away from and the sort of interaction Harmonic Serialism cannot derive turns out to be defineable in terms of abstract constraints and rankings. I also show attested cases from nasal spreading and assimilation that meet this abstract schema, and that they cannot be derived in HS. Thus, parallelism is a must to express conspiracy within violable constraint-based frameworks.