Western Mail, Thursday 24 August 1933, page 2
Here's just another example of booby traps. When our crowd was on the Somme in the '16 winter material to burn was nearly as scarce and valuable as rum. So when Fritz was eventually forced to shift his quarters a few miles rearwards there was keen competition among the boys to salvage a few bags of his coal briquettes. These were about the size and shape of an egg, and burnt splendidly.
It was only after several severe explosions had blown braziers to blazes and seriously wounded a few men, that our chaps woke up to the fact that briquettes were also the size of German bombs, a few of which the cunning beggars had mixed in with the coal - as souvenirs!