Can you imagine how is it happening? Would you think it is responding to a stimulus ?

Explanation

1) A change in the environment is stimulus.
2) The reaction of the organism to stimulus is response.
3) A stimulus is received by sense organ's receptor and produces impulses.
4) These are passed on to central nervous system and are analysed there and produce the commands.
5) These commands are carried to effector organs to show the response.