This is was my first time using an Arduino or wiring anything. Unfortunately, all the materials used were not mine so I couldn't make it permanent. However, I though it was an effective, albeit expensive, way to make a bear react to a belly squeeze. It would also make an adorable gift if you had a little extra money and could maybe add sound.

What you'll need.
-Arduino (If this was permanent I would suggest something other than the MEGA)
-wires
-resistors
-flex sensors
-thread and needle
-scissors
-hammer and nail
-something clear and plastic
-batteries or power source
-Teddy Bear

Step 1: Find a Stuffed Animal

I would suggest something with a belly to squeeze. The whole point is that its react well to the natural belly squeeze. It also has to be big enough to house the flex sensors, Arduino, and batteries. I would just make sure its big enough that an Altoid can could fit inside it with enough room to not be too noticeable.

Step 2: Prep Your Bear.

Begin by cutting his along the side of the bears belly and removing some of the stuffing. I only took out as much as I needed to work. Next, I cut hole in the front of his chest with a pair of scissor and sewed up the edges to prevent it coming apart.

Step 3: Add His Little Plastic Window

This is the part where you add his little plastic window. I used the bag of a paperclip package, but this is a part where you can get creative, perhaps a different color or shape. Once I cut it out, took a hammer and a nail and went around the edge puncturing little holes so it could be sewn into the bear.

Step 4: Creating the Belly Squeeze Sensor

Now, it is time to create the sensor that will react to the belly squeezes. I would recommend arranging the flex sensors so that, in there resting position, they aren't too bent. The reading from them seem to be much less predictable once you get to a certain degree. As mentioned before, this is my first time using an Arduino, and moreover my first time wiring anything. Don't copy this without making sure it works with what you are using.

Step 5: Program the Arduino

This is my intro to C++ quality program that i used to get him to turn on and off from the squeeze of his belly.This outline worked to get me the values I needed from the serial port and have it react consistently. Notice that instead of having it react when certain values are exceeded, I found out what the rest values were, and I had it react only when each sensor was off that value. This seemed to work way more reliably than the other combinations I tried.
The program can be viewed below. I would love suggestions. I'm new when it comes to this stuff.