At some point during your trips, your bag might get inspected by a detection dog, often looking for illegal drugs. These dogs are really skilled and can detect even tiny traces of drugs.
It is very important that your bag and its content have never been in contact with any drugs:
* Do not buy a second-hand bag from an unknown source for international traveling. If the bag had drug inside at one point, it can be detected by dogs.
* Do not pack unknown content.
* Do not pack clothes that have been in contact with marijuana smoke.
And of course, don't bring any illegal drugs with you. In some countries, possession of even small amounts of drugs can have serious consequences. Stay out of trouble kids.