Within the communication variable of the marketing (remember that there are 4: product, price, travel and promotion), advertising occupies the place to which enormous importance is attributed at the business level.
More than importance, it is taken into account the fact that thanks to communication (and advertising), the company is able to share with its target whatever you want. However, in order to do this, you must respect certain rules and laws that limit the actions that a company can take.
Specifically, subliminal advertising is a type of illicit advertising and is "... that which, because it is emitted with stimuli at the threshold of sensitivity, is not consciously perceived" (Advertising Law of Spain 1988). In summary, this type of advertising tries to affect the individual in an almost imperceptible way and thus generate positions favorable to their final purchase decision.
Some examples or actions that incite to be subliminal are given by including in the advertisement some audiovisual fragments that the eye is not able to see, but there has been enough time for this information to be retained in the brain. These images have been exposed under the threshold of consciousness of the human being, which allows directing their audience towards a more favorable purchase probability.
Another example of subliminal advertising is to include little visible or imperceptible fragments that include certain information or illegal content. In this way, and as we are barely aware of it, we do not realize its existence, but the brain does retain said information, being enough to generate a call to action.
In short, there are many ways to create subliminal advertising. They can be found in hidden images, texts with double meanings, lights and sounds, light sounds, songs, people's movements, objects positioned in a certain way, drawings that hide a message, etc ...