MSM links create traffic spikes. There is a (somewhat small) spike in August that pg attributed to a PC World article. See http://news.ycombinator.com/item?id=2865985 and the article here http://www.pcworld.com/article/237616/baseball_bat_sales_ris...
Perhaps the Dec spike is from the Inquirer article which links to HN. http://www.theinquirer.net/inquirer/news/2130668/facebook-pr...