Local (Australian) reptile keeper Simon Kortlang has held Storr's Monitors Varanus storri for many years. In north Queensland (Australia), where the species occurs they are forced to dig through hard packed dirt to get under the rocks they tend to shelter under. Kortlang's monitors were spared the trouble of having to dig through dirt to get under the rocks in their cage. Instead they merely had to move some loosely packed gravel. 

The result was no wear on the toenails. Consequently over time they grew so long that the nails curled under, in a manner not unlike humans who grow their nails excessively long. A problem faced by the monitors was that sometimes they'd tangle their feet and need human assistance to untangle them. (See photo published in The Reptilian Magazine of a V. storri’s long toenails)

Raymond Hoser has been an active herpetologist for about 30 years and published over 150 papers in journals worldwide and nine books.