ability
Stimuli is the plural form of "stimulus," which means something that is intended to enact a reaction in an organism.
If you mean "What is an organism's reaction to physical stimuli? it is usually withdrawal or avoidance. It depends on what type of stimuli and what type of organism. Is the organism used to this type of stimuli? Is it a new strange stimuli? The question is not specific enough to answer thoroughly nor is it grammatically correct.
reaction
You will have a reaction, but much lower than if you were eating them yourself. If you have a strong reaction to mushrooms you could lower the reactions by having him/her brush their teeth.
reaction to unpleasant stimuli, and observation of the reaction of others to unpleasantness or pain.
dick
puss
Perception is a cognitive process. There are several steps starting from stimuli reception to reaction of the perciver.
Caffeine increases the reaction time to visual and auditory stimuli
when an something dies like a person or a animal mother-nature/mushrooms will grow on it the dead corps
Fundamentally the system involved in a reaction to a stimuli is the nervous system.