Understanding your Chameleon
Pacing or scratching at the front of a cage
The chameleons are "asking" to get out. They are uncomfortable for some reason (lighting, temperature, humidity).
Suggestions: You should let them out and check those conditions important to them. If it is an all glass enclosure this could also be related to a lack of good air circulation. Another drawback to glass cages is chameleons do not understand reflections and stress easily when they see their own and perceive it as "another chameleon" (talk about being afraid of your own shadow).
Head bobbing is used to claim territory.
If the chameleon sees another chameleon in the area they may start bobbing their head. This is also practiced before mating. The colors are a good indicator of reason; vivid colors are shown if it is being done as a part of mating.
Gaping mouth with dark colors and hissing
They're angry about something.
Gaping mouth with pale colors
This is a sign of over heating. Cool the cage and chameleon with a good misting and adjust lighting if necessary.
Closing the eyes for long periods of time during the day
SIGN OF ILLNESS.
Bright vivid colors without dark spots
This means contentment or excitement.
Pale colors, tail coiled, jaw resting
This means the chameleon is sleeping or resting.