8x8x8 is not large enough for 6 rats with no food or water. If this is a regular thing that you do, you are extremely lucky that the rats haven't cannibalized or escaped before. A cardboard box is not something to keep rats in for more than a quick trip.
Rats will cannibalize for food and water. In the case of feeders that have been kept overcrowded and without enough food or water stress will increase the chances of cannibalism.
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