It's not funny. Dogs can die from Cannabis toxicity. You need to watch your dog very carefully.
Realistically, if the amount was significant you should get the dog to a vet immediately, as watching for symptoms of toxicity may make it too late.
Toxin
Tetrahydrocannabinol (THC)
Source
Hashish, marijuana, and hemp,
Cannabis.
General Information
Pets are more commonly poisoned from marijuana through ingestion other than inhalation. THC is the toxin that causes the symptoms and is absorbed quickly after ingestion. THC has strong antiemetic effects which make it difficult to successfully induce vomiting to remove the toxin from the pet. Most animals will recover, but it may take 1-3 days.
Toxic Dose
Depends on the concentration of THC and the form of marijuana ingested.
Signs
Ataxia, dilated pupils, 'glazed' eyes, drop in body temperature, increase or decrease in heart rate, bizarre behavior, hyperesthesia, disorientation, somnolence, depression (may last 18-36 hours), coma, excitation is seen occasionally, drooling, tremors, respiratory depression, or death.
Immediate Action
Induce vomiting. Seek veterinary attention.
Veterinary Care
General treatment: The induction of vomiting may be continued, gastric lavage is performed, and
activated charcoal is administered.
Supportive treatment: The temperature, pulse, and respiration are monitored and different medications are given depending upon the signs present. A safe environment should be provided where the pet cannot hurt itself or others while disorientated.
Specific treatment: Unavailable. To confirm the diagnosis, urine levels of THC can be determined in the laboratory.
Prognosis
Fair