This study investigates learners’ processing of English unaccusative verbs in the inchoative frame ( The door opened; Oil is spilling). Previous approaches explained L2 difficulty with the inchoative construction in terms of learners’ L1 and their perception of discourse or semantic factors hypothesized to be responsible for common overpassivization errors ( The door was opened). The purpose of the present study is to complement the extant inventory by proposing an additional factor instrumental in L2 processing. It is hypothesized that L2 use of unaccusative verbs is contingent on learners’ familiarity with formulaic expressions exemplifying the inchoative construction. The study focuses on the entrenchment of frequent phrases like My jaw dropped in Czech and Polish learners. In a lexical decision task, their reaction times for frequent expressions were found to be faster and fewer mistakes were made than in the case of non-formulaic counterparts ( My hair dropped).