Amazon.com's (AMZN -1.64%) income tax expense has been rising recently, and despite a relatively tax-efficient first quarter of 2013, the company is seeing a significantly higher tax expense than its peers as a trend over several of its most recent business quarters. In the accompanying video, Fool contributor Asit Sharma explains what's driving Amazon's income tax expense, an overlooked aspect of the company's income statement. This is the second in a series of articles examining Amazon's lofty valuation; you can check out the first article here.