beds with humans on them are hostile environment for snakes , humans move , venemous snakes can see the heat coming out and they know that they are alive and they get frustrated especially if they cannot leave or the human they are stuck with is moving or even breathing hard , a simple move might make the snake attack .
yes the baby did move only his fingers + breathing in the video but for some very angry provoqued snakes thats enough for them to attack , the one in the trailer was in a sack for a long time , enough for it to get angry and to attack the first thing it see as a reaction of self defense , ( watch how venemous snakes react in real life when they try to remove them from their sack ) .
also snakes were used to kill toddlers in history ( check history of china and ottomans and the arabs , the world doesnt turn around the west , if it didnt happen in england or france it doest mean it never did elsewhere ) .