It's fat hen (Chenopodium album). Looking up its proper (Latin) name I found this -

"Fat-hen was eaten as a vegetable from Neolithic times until the 16th century when it was replaced in the diet by spinach and cabbage. It is rich in vitamin C. The seeds were ground into flour. In Canada, it was grown as food for pigs and sheep. Although it can contain potentially harmful levels of nitrates, cases of poisoning are rare. It is very efficient at extracting nutrients from the soil. Fat-hen is an important constituent in the diet of farmland birds. The leaves are a source of ascaridole, an oil used to treat infestations of round worms and hook worms."

I knew animals like to eat it.

We know it as goosefoot in the States--heaven knows why! : )