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Last Word is ¿ìè¶ÌÊÓƵ’s long-running series in which readers give scientific answers to each other’s questions, ranging from the minutiae of everyday life to absurd astronomical hypotheticals. To answer a question or ask a new one, email lastword@newscientist.com

Does a full moon reflect enough sunlight to drive photosynthesis? Is there a cut-off point below which the process simply stops?

Pat Sheil

Sydney, Australia

I recently lost my dog and good friend, Milou, to old age. I cry a lot for him, and it made me wonder: why does crying help us so much?

Mike Egan

Meath, Ireland

To answer this question – or ask a new one – email lastword@newscientist.com.

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