Your baby at this stage interprets your expressions and actions pretty well. Agree or not 'No' is perhaps one word that you tend to overuse with your kid, no matter even if they are few months old. 'No touching the box', ' no touching the switch', ' don't eat that', 'don't throw that,' etc. In reality hearing repeated "No" has a huge effect on your baby.
What you need to know
Understand the fact that 'No' has different effect on kids of different age group. Your baby is just around eight months, and this is the time which is considered as the beginning of his language skills. So, anything you say or do will be mimicked, and actually will come back to you. Saying 'No' more often allows the child also to say 'no' to anything you ask him to do. This is because he files your reaction to his doings in his brain in a such a way that 'no' seems to him the most plausible answer that needs to be given in any situation.
To reiterate, your baby might throw purposefully and wait for your response. Your 'no' confirms again and again that this is what needs to be done. Hence, make it to point to learn to say 'no' without actually saying 'no'.