"Yawning" most of the time seems to just be a way to realign the lower jaw.
Flicking of the tongue as well know is used from smell... that's just it! Smell... if you place something new in a snakes cage it will become interested and smell it... the flicking of a snakes tongue is similar to you moving your arms while walking, you don't consciously do it and if needed, you can manipulate that movement to your advantage. (I've never seen a snake move without the flicking of it's tongue**)
If you've disturbed your snake from a resting period and it is startled it will do one or a combination of things.
- rattle tail
-deflect your hand from any area touched
-strike
-flee
Curious snakes usually become curious when there is something to be curious about... i.e. something new... new cage, new cage fixture, new person holding them, in general new smells.
A snake would become alert for various reasons
- mate
- threat/enemy
- prey
- etc...
Alertness can vary from lack of movement to excitement, it all depends on the stimulus...
if you take the time to observe your animal yo can unmask their "personality"
hope that helped...
~ZF

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Royal ReptileZ