In order to make the frog feel real each body part was added as a separate entity and revolute joints were employed to connect the body parts to each other in the positions shown below:
A revolute joint connects two bodies but doesn't constrain their relative angles, which means that after adding them the frog's legs and tongue rotated like the frog had every bone in his body broken. However Farseer also provides angle limit joints, that constrain the angle between two entities. These limits can be changed after the simulation has started.
Click here for a movie showing the leaping frog. Initially the upper and lower limits of the angle joints are set to zero, so the frog is completely rigid. Each time I press a key these limits are set to something close of a real frog and an upwards force is applied to the frog body, thus making it look like a leap. Another key sets the joint limits to the initial values. It's all Farseer's work, really.
Next step is controlling the frog's leap so he'll jump from platform to platform.