From the notes accompanying the exhibit:
In the 18th century [and later according to Howells, as cited in the previous post], it was quite usual for people living in rural areas to take their dogs to church. As dogs cannot always be relied on to behave properly, many churches kept a pair of these expanding tongs handy so that they could separate aggressive animals. This pair with its iron grips would work best on long-haired, rather than short-haired dogs.I wonder what short-haired dog-tongs looked like? Tipped with felt pads perhaps?
(Thanks to Jonathan Law for the research work.)
UPDATE: When I picture these dog-tongs I see a grim but secretly amused RS Thomas wielding them. It's a not unpleasant image.