Tying a cherry stem in a knot with your tongue is a great way to show off your incredible tongue skills. Needless to say, people with skilled tongues are better kissers, better in bed, better at.. well, at all of the many uses for the tongue. So without further ado, here is my method for tying a cherry stem in a knot with your tongue:

1. Bend the stem in your mouth where it folds over, like this:

   _
  / \
  \ /
   X
  / \
 /   \
/     \

2. Press the lower end of the stem to the roof of your mouth with the back of your tongue (so it can't roll) and use the tip of your tongue to fold the other end of the stem under, toward the loop.

   _
  / \
  \ /  /
   X  /
  / \/
 /
/

3. Keep the back part pressed to the roof of your mouth with your tongue, brace the loop with your teeth, and use the tip of your tongue to push the free end through the loop.

   _
  / \
  \ X
   X \
  / \/
 /
/

4. Once then nub of the free end is through the loop, grip it with your teeth and use your tongue / lips to pull the knot tight.

 \
  \
   X\
  ( X  Congratulations! (You've made bad ASCII art!)
   X/
  /
 /

You're on your own after this. I usually spit it out on my plate or napkin when nobody's looking. You may be inclined to pull it out with your fingers, but that will make people think that there was some trickery involved, not pure tongue skill.

Alternative Method (This is technically cheating)

1. Tie a cherry stem in a knot with your fingers.
2. Slip it into your mouth when nobody is looking. Don't swallow it.
3. Get everyone's attention, and
4. Put an untied cherry stem into your mouth.
5. Churn your mouth around, like you're really working on something, then
6. Remove the previously-tied cherry stem. You can swallow the untied one if you don't want to get busted, or slip it out when you're done signing autographs and getting phone numbers from hot members of the opposite sex who are insanely attracted to you..