We know that humans and dogs share many qualities, abilities, and emotional predispositions so it shouldn’t come as a surprise to discover that humans and dogs may also share certain frailties, like substance abuse.  If you’re envisioning dogs slinking down the seedy end of town to buy their drug of choice then hiding in a dirty alley to self-administer it while running the risk of overdose, get the vision out of your mind.  However, dogs are seeking hallucinogens and risking their lives much in the same way as many human addicts.  But, in the case of dogs, the “pusher” isn’t some sleaze ball in gang colors hanging around on street corners…it’s a toad.
It seems certain toads are able to produce poisonous substances as a form of defense mechanism making their skin poisonous.  Additionally, they have parotoid glands behind their eyes which produce a substance when mixed with their sweat or water on their skin, producing a solution poisonous enough to kill a grown dog.  Ingestion of the solution can be fatal because the toad’s venom contains digoxin-like cardiac glycosides.  In America, such a poisonous toad is called the Colorado River toad.  In South America and a number of Caribbean countries and Australia, they are called “cane toads”.
The mixture of toxins includes a hallucinogen called bufotenine and its effects are much like LSD and mescaline.  Humans, who are addicted to the toad venom and ingest these substances are referred to as “toad licking”.  Bufotenine is the hallucinogenic component of the toad venom and is a controlled substance making it outlawed in many places. 
So what does this have to do with dogs?  It seems that dogs are licking these toads and it has become a world-wide problem and is epidemic in Queensland Australia.  Apparently, the toad secretions taste sweet so the dogs lick the toad and, if they survive, experience a hallucinogenic episode.  Some dogs become addicted to these psychedelic effects, increasing the number of canine repeat offenders or “serial lickers”, being treated for cane toad poisoning several times a year.  The dogs deliberately get intoxicated by the cane toads and will come back on a regular basis, licking the toad in such a way as to get a very small dose.  Some dogs are so desperate for a dose that they will hunt down these toads to stimulate the excretion of poison, which they can then lick.  But, like all addicts, these dogs are risking their lives for a momentary cheap thrill.
And you thought all you had to worry about was warts!