In the Crescian society, on alternate Earth, the nobles have a refined sport of settling disputes with mutual assassination.
The unspoken rules are that they must be carried out directly by the nobles themselves, and should a noble be ‘caught’ in the assassination process, they will be executed.
To avoid being caught in their assassination attempts, the nobles devise all sorts of methods to steathily take out their rivals, the primary means being poison.
In particular, poisons that have certain activation conditions are the most popular.
Is it possible to create a poison that is de-activated by swirling/mixing the contents of the glass, whether it is soup or drink, and how would it work? The opposite (poison triggered by stirring) is also acceptable, although a convincing reason should be given (eg. providing a layered drink that should be ‘mixed’).
Also, how to make it such that not doing this process has as close to possible a 100% chance of successfully dispatching the target, and 100% chance of surviving if the swirling/mixing is done?
Also important is how to configure it to have more minimal side-effects when de-activated.
Another good aspect to have would be slower-acting; if it is too lethal then it would give away the poison instantly, revealing the host to be the assassin and also frightening off the other guests, preventing them from consuming.
Note: We apply Artistic License: Poison, so a top-level overview of the process through which the poison is de-activated works.