Does the 'five-second rule' about dropping food really exist?
It is a common dilemma for parents at mealtimes. If your child drops some food on the floor, should you ever pick it up and give it back to them?
Many parents invoke the "five-second rule" when deciding what to do: the perception that, if the food has only been on the ground for a matter of seconds, then it is unlikely to have been badly contaminated with germs.
But is there any scientific basis to that idea - or is it just one of those parenting myths?
Sophie van Brugen went to put the theory to the test with mother Lucy Roberts and Dr Ronald Cutler of Queen Mary, University of London.
The food experiment carried out by Dr Cutler was much more extensive than we've been able to show in this finished report, and included controls which the results were compared with.
Video journalist: Dan Curtis
Listen: comedian Alun Cochrane wonders how fast germs can transfer from the floor onto food on BBC Radio 4's Alun Cochrane's Fun House