A deadly cobra slithered into a teacher's pants while he was giving a lesson to pupils on snake safety.

Wildlife expert Sitthiporn Dansirima took the reptile to assist him and colleagues during a demonstration on identifying different species at the Ban Non Sathian School in Bueng Kan, Thailand, on August 21.

However, while Sitthiporn was holding the animal by its tail, trying to make it expand its hood, it slithered towards his ankle and slipped inside his jeans.

Footage shows the calm volunteer minimising his movements to avoid scaring the snake. Another volunteer, Nong Wave, pulled down Sitthiporn's pants and eventually removed the cobra hiding in his legs.

Relieved Sitthiporn said: ‘This was the biggest lesson of my life. Even though I managed to capture the snake, I made a big mistake. Next time, I will be more careful.'

Teacher Rungrueng Tharawet said he and the other instructors were nervous when it happened.

He said: ‘The trainer could not move because the snake might bite. We were all nervous about whether he would be able to remove it.'

The teachers turned off the audio equipment and asked the youngsters not to make a sound.

He said: ‘We did everything to keep the snake from being startled. If it was scared, it could have bitten our colleague.

Nirut Chomngam, head of the local government's wildlife tear, said he was also attending the lesson and did not expect the cobra to find its way into the man's trousers.

He said: ‘Snakes generally won't attack unless they feel threatened, and they are more likely to flee due to their natural fear of humans.'

Researchers found that 7,000 people are treated for snake bites each year in Thailand. Suchai Suteparuk from the Division of Toxicology at Chulalongkorn University reported that 30 of those die, with cobras being the biggest killer.