The reason dogs get sick when they eat chocolate is because of a naturally-occurring compound in the cocoa beans called theobromine.
Theobromine is a stimulant that makes dogs very ill, and can cause damage to their central nervous system and even kill them.
Daily Mail reports that research shows dogs are poisoned by chocolate at twice the rate over the Easter weekend.
While most people know not to feed chocolate to dogs - the vet is begging owners to educate young children to not share their Easter treats with dogs. Also to keep an eye on inquisitive dogs who will try and get into the chocolate themselves.