give the gerbils a box

And don't expect to get it back. The gerbils can completely dismantle and dismember a box in less than half a day. Put the box in and they sniff around, climbing into it and scratching around. Until they realise that they can bite it. And they chomp crazily.

Like this:

Chomp...          Chomp...          and Chomp...

After that Gerby laps up the water crazily. It must be really tiring chomping all that cardboard.