When reading scientific text, readers must draw inferences when the author does not make relations explicit; readers also need to pick up on causal relations that the author "does" make explicit. We collected think-aloud protocols from 86 undergraduate biology students reading 7 brief, illustrated passages about the immune system. After reading, participants typed a free recall. Both think-aloud and recall were transcribed and coded for two types of causal language--specific action verbs and explicit causal terms (forms of the word "cause")--as well as inferences. Inferences in recalls were significantly related to action verbs picked up and during reading, as evidenced by the think-alouds. Action verbs in recalls were significantly facilitated by inferences and pick up of action verbs articulated by the participants while reading, as evidenced by the think-alouds. Explicit causal terms in recalls were significantly facilitated by pick up of action verbs while reading. Results suggest a very important role for pick-up of specific action verbs while reading, and risks associated with learners substituting vague verbs of class membership ("is a," "has a") for highly specific action verbs ("activates," "binds") when learning biology. One possible implication is that prompting students to pick up on specific action verbs while reading biology texts--in addition to making inferences during reading--could prompt more benefit from reading these types of texts.