Sometimes strange ideas come into my head. Most of the time, being too busy to act on them, I shoo them away and get on with my life. On this one occasion, though, we had a continuous metabolic measurement system already set up, and were about to use it for measuring the metabolic rate of a rat. So, for once, with the help of Thomas Förster (Senior Research Scientist at Sable Systems, which is to say he actually made the measurements and did all the hard work), I thought: What about using the system to measure photosynthesis?