You are considered in possession if you have the keys to a property that contains a drug.

You are considered to be trafficking if you possess a certain quantity of that drug.

There is a mandatory death sentence if the quantity of the drug that you "possess" for trafficking is over a certain amount. In the case of cannabis it's over 500 g.

Singapore == scary laws.

People go to prison in some countries for grains of cannabis resin stuck to the sole of their shoe even if they have no trace of cannabis in their system.