Thats called dysecdysis. It was either that or maybe his/her toes might have gotten caught on something in the cage? Is there anything in the cage that might make that possible? The nails won't grow back, but he should be fine.
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1.0.0 arg. b/w tegu
1.1.0 white's tree frog- popeye, jack
0.1.0 southern painted turtle- ms.tortle
0.1.0 crested gecko- crimson
1.0.0 pinto hedgehog- dante