A snake uses its forked tongue to collect scents and then flicks them into the Jacobson's organ on the roof of the mouth.
Take your snake on the roof and clean the drain from the vent.
The tongue is used to capture the air particles around the snake. It (the tongue) is rubbed on a small organ in the roof of the mouth called "vomeronasal organ", or "Jacobson's organ. From this the snake can perceive if there is prey or predators around it
Jacobson's organ
When a snake flicks its toungue it is gathering scents from the air, which are then sent to the Jacobson's organ at the roof of the snake's mouth. This gives it a very accurate sense of smell.
The snake flicks it's tongue to capture smell molecules carried on the air. The tongue then brushes against the Jacobson's organ inside the roof of the mouth, to annalyse the smell for possible prey or danger.
Use either a plumbers snake or a brush ( like a bottle brush or a refrigerator coil brush) Very ,very carefully as the vortex created can pull you in and drown a person quite easily .. The use of the snake should be very limited as the wire can be quite heavy when trying to retrieve it as you have the weight of the snake plus gravity fighting you On high rise building where the roof drains can be as large as 6" diameter I like using either the General Ram Jet or a water Jetter . Most of the roof drains should have some type of protection such as a dome or grate on promenade systems thus the stoppages should be soft.
When a snake flicks its tongue, it is essentially "tasting" the air. Various chemicals are picked up by the appendage that inform the snake of things like atmospheric conditions and the general direction of prey.
The Jacobson's organ is a pair of 'pockets' on the roof of the snake's mouth - that the tips of the tongue are inserted into. The two pockets are independent from each other - giving separate signals to the snake's brain. If the scent on one point of the tongue is stronger than the other, the snake knows to move in the direction the stronger scent is coming from - until it finds its prey.
Fire
A rattlesnake, like all snakes, uses its tongue to find food. The tongue of a snake is used in conjunction with the Jacobson's organ on the roof of the mouth to smell.
It's a 'sensory organ'. It basically takes the form of two 'pockets' in the roof of the snakes mouth. When the snake flicks out its tongue, microscopic scent particles stick to it. Withdrawing the tongue back into its mouth, the tips are inserted into the Jacobson's organ, and the snake's brain decodes the information.