Since fall of 2005 a course blog has been used in introductory physics courses at Creighton University to discuss real-world applications of physics and engage students in discussion and thinking outside of class. Specifically, the blog was created to address elements of the "hidden curriculum" that are difficult to cover in class, and a previous work showed that students who posted to and read the blog did not suffer a deterioration in attitude/expectations as seen elsewhere using the MPEX or CLASS instrument. Here we analyze the content of student posts to the blog along several dimensions: student interactivity, the introduction of new knowledge, application of knowledge to real-life situations or other disciplines, self-disclosure of prior knowledge, and fascination/interest. Students' online discussion behavior is analyzed and compared to results on the FMCE (The Force and Motion Conceptual Evaluation) to determine if certain types of discussion behavior are correlated with student learning. We also present several interesting gender differences in students' online discussion behaviors.