If you want to see how flexible your trunk is, there is a really simple test you can do. I learned this from my friend and he helped me with it the first time.
You need to first draw a line on the wall with a pencil and it needs to be vertical. Stand in front of that line with your back to the line and make sure to leave space between you and the wall. Hold your arms straight in front of you, and without moving your feet, twist your trunk to the right until you touch the wall and have your friend mark that spot. Do the same towards the left. If the mark is before the vertical line, it's a negative point, if it's after, it's a positive. You need to measure the distance between the marks and the vertical line and take an average.
If the average of the two distances is 15-20 centimeters, that means you are very flexible. If it is between 0-5 centimeters, your trunk is not very flexible.