The blue-footed booby (pictured) is an extraordinary-looking bird. It has fairly dull plumage but strikingly coloured blue legs and feet. What could be the evolutionary benefit of such a conspicuous feature? Both sexes have blue feet so they don't seem to be for impressing potential mates.

Sam Moore, London, UK

The colour Blue seems to be a rarity among land animals - mammals especially (we never see a blue cow or a blue dog and so on; only birds and fish display blue)  - is there a reason for this?

I made a salad dressing with olive oil, apple cider vinegar, garlic cloves chopped into halves, fresh ginger, mixed herbs and mustard powder. When the dressing was finished I put a lidded jar of it in the fridge, and two days later topped it up again with fresh ingredients.

The following day the garlic from the original batch had turned bright blue. Why?

Ellice Bourke, Katherine, Northern Territory, Australia