Someone once told me that as a college student he/she wanted to try LSD because he/she was told that one could taste blue (apparently she really wanted to taste blue). Anyways, I think hearing lightening and seeing thunder has very similar relationship with tasting blue. I can definetly see how the drug can temporarily switch/play with the brain to cause senses to switch. However, since most of us have never gone down that path (I think), it is hard for us to really understand people who have experienced synesthesia. Just because we haven't experienced it doesnt mean it doesn't exist.