SUBREDDIT: r/AskReddit
TITLE: I need ideas for a double-blind placebo experiment simulation with college students. May God pay you with lots of karma if you can help me!
POST: I am researcher at a R&D Center in a european university. Tomorrow I am receiving the visit of students of a nearby college to talk about what is our job as researchers and what we do in our Center. I have about an hour to talk and also thought of talking a little about the scientific method, blind experiments and placebo effect. 

I think it would be fun and more easy for them to grasp the concept to have a real experiment conducted with the students, so I would enjoy some ideas for a double-blind placebo controlled experiment that can be conducted in under 30 minutes. 
I had prepared something related to short term memory and numbers, to test if it can be improved with the association of images, but I would like to come up with something more clear.

In my idea, I will separete students in three groups, will give each group a separate set of instructions to read, and will show them two strings of 9 digit numbers. After one minute will ask them to write the numbers down:

Group 1 - control group. Instructions are blank.

Group 2 - placebo group. Instructions are to read the numbers to themselves and repeat them until the time is passed. (Hypothesis is that this is what a person without any other strategy does anyway)

Group 3 - experimental group. Instructions are to think of the numbers as images that I will provide them (1 as a walking stick, 2 as a swan, and so on), and construct a visual string of images with the digits of the numbers)

As you can see it is not a very good idea, it has several shortcomings such as placebo and control groups being not really well constructed.

Any better ideas??????
TL;DR: 
I would like to put some college students through a real double blind placebo controlled experiment. I will talk to them for one hour tomorrow in a visit to my university. Any ideas??