Snails - hibernating

So far it has been a mild winter. We often use old house bricks to balance the flowerpots on. This serves two purposes - it increases the height of the pots and helps prevent them from being attacked by slugs and snails (at least sometimes). We have been cleaning out around the pots when this clutch of snails were spied squashed in the airspaces of one of the bricks. This is the first time that I have ever witnessed snails hibernating!