On land, the adult frog has pulmonary respiration only.

Frogs also have a respiratory surface on the lining of their mouth on which gas exchange takes place readily. While at rest, this process is their predominate form of breathing, only fills the lungs occasionally. This is because the lungs, which only adults have, are poorly developed.

Explanation:

your body is trying to warm itself up. or more precisely, sensors in your skin send messages to your brain to generate heat to your body.