What are the signal words and phrases in left over and tracers

The Text for this is

Explanation:

In 1910, just before Marie Curie collected her second Nobel Prize for radioactivity, young György Hevesy arrived in England to study radioactivity himself. His university’s lab director in Manchester, Ernest Rutherford, immediately assigned Hevesy the Herculean task of separating out radioactive atoms from nonradioactive atoms inside blocks of lead. Actually, it turned out to be not Herculean but impossible. Rutherford had assumed the radioactive atoms, known as radium-D, were a unique substance. In fact, radium-D was radioactive lead and therefore could not be separated chemically. Ignorant of this, Hevesy wasted two years tediously trying to tease lead and radium-D apart before giving up.

Hevesy—a bald, droopy-cheeked, mustached aristocrat from Hungary—also faced domestic frustrations. Hevesy was far from home and used to savory Hungarian food, not the English cooking at his boardinghouse. After noticing patterns in the meals served there, Hevesy grew suspicious that, like a high school cafeteria recycling Monday’s hamburgers into Thursday’s beef chili, his landlady’s “fresh” daily meat was anything but. When confronted, she denied this, so Hevesy decided to seek proof.

Miraculously, he’d achieved a breakthrough in the lab around that time. He still couldn’t separate radium-D, but he realized he could flip that to his advantage. He’d begun musing over the possibility of injecting minute quantities of dissolved lead into a living creature and then tracing the element’s path, since the creature would metabolize the radioactive and nonradioactive lead the same way, and the radium-D would emit beacons of radioactivity as it moved. If this worked, he could actually track molecules inside veins and organs, an unprecedented degree of resolution.

Before he tried this on a living being, Hevesy decided to test his idea on the tissue of a nonliving being, a test with an ulterior motive. He took too much meat at dinner one night and, when the landlady’s back was turned, sprinkled “hot” lead over it. She gathered his leftovers as normal, and the next day Hevesy brought home a newfangled radiation detector from his lab buddy, Hans Geiger. Sure enough, when he waved it over that night’s goulash, Geiger’s counter went furious: click-click-click-click. Hevesy confronted his landlady with the evidence. But, being a scientific romantic, Hevesy no doubt laid it on thick as he explained the mysteries of radioactivity. In fact, the landlady was so charmed to be caught so cleverly, with the latest tools of forensic science, she didn’t even get mad. There’s no historical record of whether she altered her menu, however.

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