Sentence:  Some of the sad, intriguing varieties-of this phenomenon which have been documented in Nigeria include: (i) Illegal exchange of information, written or verbal (for example, by copying or giraffing,' use of drums, flutes and <WSD>bio-codes</WSD> such as coughing, sneezing and whistling) to help candidates answer objective questions. 
Meaning of the word marked with <WSD> tags:  A signal consisting of a biological action.