Ini disebabkan karena kesulitan dalam mekanisme pemilihan substansi-substansi kimia yang memberikan informasi rasa dan bau tertentu misalnya rasa manis, pahit, asin, bau wangi, busuk.
It is because of difficulties in choosing mechanism of chemical substances which provide information for certain taste and smell such as sweet, bitter, salt, fragrant aroma and reek.