I am imagining a creature (whatsoever) that could produce an other type of saliva when needed.
it can produce normal saliva to ease digestion, but it can also produce, when needed, a strange type of jelly, an explosive type of saliva that it can spit.
Therefore, I have absolutely NO IDEA how the saliva could explode (the explosive solution that he produces would explode in contact with air but i don't know how). To not harm the creature, I thought that the explosive saliva could be surrounded with a mucus made of lots of bubbles. When the creature spits the special saliva, bubbles that surround the explosive saliva bursts when it hits the target, so the saliva is in direct contact with the air, it then "explodes". Or, let's say the creature wants to blow up the base of a tree. I thought he could stick the explosive saliva (yes, the saliva should have sticky properties) onto the tree trunk and wait for the protective mucus to dissolve (in a matter of more or less 30 seconds) for the saliva to explode.
Now here are the required points:
-explosive saliva that can be released when needed (from a pouch inside), and normal saliva would be produced normally, when the creature doesn't use the detonating one.
-a protective mucus composed of bubbles that surrounds the explosive saliva which bursts if the creature spits hard enough, or naturally dissolves itself in a matter of 30 seconds, allowing after the explosive saliva to explode. (Or if you can, find something that ables the special saliva to explode when far away from the creature, and can act like a timer-bomb, that's the only solution i've found).
-the explosive saliva to explode in contact with air. what will it be made of? If it isn't possible, be free to find something else.
-the explosive saliva to be sticky.( I thought that it would stay liquid when in contact with the normal saliva in the creatures mouth, but when it isn't anymore, it becomes sticky. feel free to find an other solution.
I hope you will find a solution that requires all the criterias (if not possible, it's fine).