The Food Standards Agency is investigating urgently how a number of beef products on sale in the UK and Republic of Ireland came to contain some traces of horse and pig DNA.
The horsemeat scandal demonstrates how long and complicated the food chain we all depend on is. Regulating our food supply is expensive.
Some of the best, and worst, jokes and gags from Twitter users discussing the discovery of horse DNA in some supermarket beef burgers.
We've seen the jokes on Twitter but the discovery of horse and pig DNA in beefburgers poses a serious question; where did it come from?