Where is your sensitive part?

Today I had my Biology practical exam.
I can't find another word to describe it except...hm...ridiculous.

Qn: Find out which part of our body is most sensitive to touch.

So, how are you going to plan an experiment like that?

1st step
Aim: To find out which part of my friend's body is most sensitive to touch.

2nd step
constant variables:
1) same pressure applied to the skin
2) same friend

3rd step
apparatus:
1) U shaped paper clip - for poking your friend
2) fine tipped marker - to draw dots on your friend
and the most important one
3) a friend - for you to poke

After written all the procedures and data and bla bla bla, here's the final step.

last step
experimental error：
This is tricky, cos I can't think of a better answer than' I can't ensure that my friend didn't lie when I poked her'.
And of course, the assumption made is ' I assume that my friend did not pretend to be in pain when I poked her'.

Well, you think I really wrote that?
No one will be stupid enough to write that for mid year exam.

So if the practical is not ridiculous, then find me a better word, and fill in the blank below：

I solemnly swear that I think the practical is:__________.