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Twenty-five people have been hospitalized in Germany after eating sandwiches laced with rat poison, police said Wednesday.

So far none of those hospitalized has shown symptoms of illness but they are being kept under observation as a precautionary measure, said police spokesman Frank Soika.

The sandwiches and a note saying they were a gift had been left on the doorstep of an auto parts company in the northwestern town of Steinfeld on Tuesday.

Employees helped themselves to the sandwiches before someone noticed a strange substance on them.

A Berlin laboratory confirmed overnight that the food had been sprinkled with rat poison, Soika said.

"We don't believe the amount of poison used would have been deadly, but it could have caused serious illness," he said.

Police have no indication yet who left the sandwiches or why.