References to maritime forms, natural objects and shells can observed in many works of Borromini’s and go far beyond the usual baroque fascination with natural serpentinatae. This essay investigates how the geometry of a shell, its haptic value, its plasticity relates to the constructive principles that govern San Carlino’s curves and protrusions, its fractured forms, its cracks and collisions of elements, its spatial inversions, overlappings and amalgamation. It argues that the seashells - stored prominently in Borromini’s house - have served as a starting point of a methodological shift: a formal, spatial and haptic inculabulum in a design process that revolved around clashes between classic determinist mathematical systems and chance. San Carlino is an early form of an intense, phagic architectural collage: The structure swallows the Tiber Fountain, squeezes around the cut-off corner, soaks up the later-added main facade, forming an intense image of superimposition, exacerbated compression and of hyper-plastic excentricity, like the Xenophora snail that collects other shells, objects and occasional debris and cements the pieces into its own shell. In Borromini’s work, the seashells trigger a new way to encompass the role of haptics, color, sound, surface spatiality, and ‘porosity’ in architecture, and a new form of aesthetic freedom.