The Australians and New Zealanders guard the borders of their island nations zealously against any potential infestation that might damage their crops or, in this case, livestock.
The Aussies are quite proud of their latest bust, a passenger transporting two sausage and egg McMuffins from Bali, Indonesia, where there's been an outbreak of foot-and-mouth disease, to Darwin, Australia. The smuggling passenger was caught by a sniffer dog and fined the equivalent of US $1,870.
Gary Leff has the details here in View From the Wing.
It can happen here too, and probably does every day, but only a few cases get publicity. For example, in 2018 a Minnesota woman was fined $500 and lost her Global Entry status for failing to declare an apple to U.S. Customs, an apple Delta Airlines had handed out inflight.
In August 2015 granddaughter Avery and we personally witnessed an acrimonious exchange at U.S. Customs after landing from Paris at Newark Airport (EWR). A woman pushing an infant in a stroller was complaining loudly to the customs agent because he had faulted her for not declaring the baby's bottle of milk. He had the last loud word as he was leading them away. "You've just lost your Global Entry!" It doesn't pay to argue with a New Jersey customs agent.
For what it's worth, we avoid carrying food across borders, unless it's something like aged Parmesan Cheese from Parma that a) we know is legal to import, and b) we intend to declare.