The first ever paid job I did, between the 5th and 6th forms at school, was at a pork pie factory where, among other products, we made pies for M&S.
The bushes by the factory's canteen were covered in massive hairy caterpillars. Hundreds of them got added, courtesy of mischievous hands, into the M&S pies (and no others, because only the best would do) but, unless they managed to keep it very quiet, there wasn't a single complaint received from any customer!
Is it the Mexicans who put a caterpillar in some bottles of tequila?
A M&S customer coming across an unexpected body in their meat pie might think it nothing more than an exotic bonus.