This paper explores the processes underlying verb metaphoric extension. Work on metaphor processing has largely focused on noun metaphor, despite evidence that verb metaphor is more common. Across three experiments, we collected paraphrases of simple intransitive sentences varying in semantic strain--for example, "The motor complained" [right arrow] "The engine made strange noises"--and assessed the degree of meaning change for the noun and the verb. We developed a novel methodology for this assessment using word2vec. In Experiments 1 and 2, we found that (a) under semantic strain, verb meanings were more likely to be adjusted than noun meanings; (b) the degree of verb meaning adjustment--but not noun meaning adjustment--increased with semantic strain; and (c) verb meaning extension is primarily driven by online adjustment, although sense selection also plays a role. In Experiment 3, we replicated the word2vec results with an assessment using human subjects. The results further showed that nouns and verbs change meaning in qualitatively different ways, with verbs more likely to change meaning metaphorically and nouns more likely to change meaning taxonomically or metonymically. These findings bear on the origin and processing of verb metaphors and provide a link between online sentence processing and diachronic change over language evolution.