The dryness is not a problem, any more than dry grains are a problem.
The issue is with beans that have not been cooked. Cooked is fine, whether they are wet or dry, but raw is not.
Raw beans have a toxin that is destroyed by the heat of cooking. It affects people too, except that we usually cook our beans

Some beans have more than others, but there is no convenient way to check how much is in what beans, so the usual advice is to cook them all (for humans and for chickens.)
A quote about the effects in people:
"Poisoning can be induced from as few as four raw beans. Symptoms usually begin with extreme nausea and vomiting within one to three hours of ingestion, followed by diarrhea. Abdominal pain has been reported in some people. Recovery is usually spontaneous and rapid, occurring within three to four hours after onset of symptoms, although some cases have required hospitalization."
Source:
https://en.wikipedia.org/wiki/Phytohaemagglutinin