Yes, Mother-in-Law is toxic to dogs!
Dogs accidentally consuming the Mother-in-Law 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).
Mother-in-Law consumption is also toxic to Cats.
Toxic Principles Of Mother-in-Law: Calcium oxalate crystals.
More Info About The Mother-in-Law Plant
Scientific Name: Monstera deliciosa
Family: Araceae.
The answer is based on information found on The American Society for the Prevention of Cruelty to Animals (ASPCA) website.