There was a tiny hole in the Snickers bar wrapper.
North Salinas police say the piece of candy was given to a 16-month-old trick-or-treater.
However, the girl's mother ate it. She almost immediately started to feel sick and went to the emergency room.
Officials believe some kind of drug, like LSD, was injected into the chocolate.
"With that kind of strength, I almost shudder to think what could have happened to my niece, it would have been far too strong of a dosage for a toddler," the victim's brother said.
Police believe this was an isolated incident. They are looking for the person who might have tainted the candy and if it was intentional.
Police remind parents to check their children's Halloween candy.