"At college I'd seen my dead frog's limbs twitch under some applied stimulus or other - seen, but hadn't believed. Didn't dream of thinking beyond or around what I saw"

This quote is most likely referring to a college biology class, where the speaker saw a dead frog's limbs jerk under some sort of stimulus. The speaker was most likely shocked by this, as they had not expected the dead frog to move. The speaker was most likely unable to comprehend what they were seeing, and did not believe to question it or search for an explanation. This quote could be interpreted as a metaphor for the speaker's own life, where they had actually seen things that were unanticipated and unexplainable, but had actually not taken the time to believe beyond or around what they were seeing. It could be a tip to put in the time to look for explanations and to think more deeply about the important things that we experience.