The Clever Hans Effect has also been observed in drug-sniffing dogs. A study at University of California, Davis revealed that cues can be telegraphed by the handler to the dogs, resulting in false positives. A 2004 study of Rico, a border collie reported by his owners as having a vocabulary of over 200 words, avoided the Clever Hans effect by having the owner ask the dog to fetch items from an adjacent room, so that the owner could not provide real time feedback while the dog was selecting an object.