Jídlo is the regular way to say food. Žrádlo is very informal and may even be derogatory, which is why it's used for animal food here.
Žrádlo is not really derogatory or informal when used for animal food. Just don't use it for food intended for human consumption. The same applies for verbs: žrát vs jíst. It's similar to German fressen vs essen.
Nothing, but we have a report, which is probably yours according to the timestamp, which contains "dug" instead of "dog". It is hard to say, what is a typo and what an error for the Duolingo marking software.