Another possibility is a Respiratory Infection. From your description it sounds exactly like what my BP did when she had an RI. When she "coughed" (snakes can't cough, but it looks similar), she "struck".

However, if it was clear and liquid, not slimey/sticky, it was probably just water being "coughed" up in a similar way. Another member of the site posted a video of his Retic I believe, doig just this. I hope your baby burm is okay!