In Houston, he sniffer dogs are always walking around you, and sniffing you and your carry on luggage, and then your checked luggage. It is hard to tell, if they are using profile, random, or every some many by count. Always be safe, and do not carry anything that is not allowed. If you have cigarettes in your carryon, going thru xray, they will want to open your bag, and they will also do a controlled substance check on the bag, and or your purse.