See here the Common Vetch (Vicia segetalis). It is not difficult at all to find it, even if it is not that common. In many grassy spots its butterfly-like flowers abound. It grows also in cereal fields. Many grasslands in Perigord in former times were cereal fields, so maybe that is an explanation.
Every leaf is divided in a dozen or so of smaller folioles and ends in a twisted tendril. The plant climbs in grass stems and other stalks and attaches itself with those tendrils
On the left in the photograph you see a vetch with smaller and narrower folioles, this is another species and it is called Hairy Tare (Vicia hirsuta).