Yes, Cuckoo-pint is toxic to dogs!
Dogs accidentally consuming the Cuckoo-pint plants can show the following clinical symptoms: Vomiting, Prolonged Depression, Incoordination, Hypersalivaton, Sleepiness Or Excitation, Dilated Pupils, Low Body Temperature, Low Blood Pressure, Coma, Seizure And Death (In Rare Cases).
Cuckoo-pint consumption is also toxic to Cats and Horses.
Toxic Principles Of Cuckoo-pint: Insoluble calcium oxalates.
More Info About The Cuckoo-pint Plant
Scientific Name: Arum maculatum
Family: Araceae.
Also known as: Arum, Lord-and-Ladies, Adam-and-Eve, Starch Root, Bobbins, Wake Robin.
The answer is based on information found on The American Society for the Prevention of Cruelty to Animals (ASPCA) website.