Nitrogen compounds, like urea, a big component of urine, are transformed over several steps.

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In a 2011 ruling, Duffy wrote that while Yousef was awaiting trial, he had been trying to collect urea -- a component of urine -- and a type of watch that had been used in a detonator in the airline bomb plot.

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Indeed, a calculation Dr Ip performed, based on the volume and composition of the urine he collected in the plastic buckets, and of the head-dunking water at the end of each day, suggested that only 6% of the urea excreted by the turtles was leaving them in the traditional manner, via urine.

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