Trombone to French Horn?

Q: How do you make a trombone sound like a french horn?
A: Stick your hand in the bell and play lots of wrong notes.

French Horn to Trombone

Q: How do you make a french horn sound like a trombone?
A: Take your hand out of the bell and lose all sense of taste.

Trombone Testing

Q: What is the difference between a trombone and a trumpet?
A: A trombone will bend before it breaks.