We buried an old boat and fill with water for my ducks to swim in. The whole front hull underneath had a styrofoam liner. I could hear them nibbling on it (drove my dog absolutely crazy! Like fingernails on a chalkboard) lol. Eventually they broke it loose and a big section fell out. When i picked up the chunk that was left, it was pretty obvious they had probably ingested some. Apparently they pooped it back out, as I never had any issues.