Adri frowns. "This doesn't tell us what we really need to know. Which is - has Foster had a greater metabolism rate than normal in the last few days? Because, if he did, he'd be using more oxygen."

"Let me resort Samara's data," you say. You make a few mouse clicks, and a new chart appears on the screen.

"Hmmm," Adri says. "Looks like Foster's metabolism has actually been slower than usual in the last few days. Less energy output than Samara, that's for sure."

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