On Tuesday morning zoo keeper Marek Zdansky was conducting a routine check of the run at the gorilla compound at Prague Zoo when he made an alarming discovery: five large red apples studded with steel nails. Luckily, the zoo's six gorillas - including Richard, "winner" of the Big Brother parody show - were inside at the time, because it was raining.
"I would put whoever left those apples here in a cage with Richard and let them sort it out between themselves," said Zdansky.
Tuesday's incident was not the first of its kind. A year and a half ago similarly doctored apples were found in the zoo's antelopes enclosure. This time they could perhaps have posed a greater danger to Richard and co. - apples are among the great ape's favourite foods.
"If they swallowed nails their lives would be definitely be in danger - in the worst possible scenario the nails could have perforated their stomachs or intestines," said Pavel Brandl, who is in charge of Prague Zoo's gorilla compound.
The shocking, and as yet unexplained, attempt to harm them uncovered on Tuesday fortunately came to nothing. But what can officials do to prevent repeat "attacks"?
"Prague Zoo is modern and doesn't have bars. Therefore we appeal to visitors to report any suspicious behaviour," said Vit Kahle, the zoo's spokesman.