A five-year-old Shropshire boy discovered a live two-foot snake in his box of breakfast cereal.
Corn snakes can grow up to 6ft long
Jordan Willett, from Dawley, found the corn snake inside the packet of Golden Puffs on Bank Holiday Monday.
His mother Theresa, 23, said he was still in shock and not eating. The cereal was bought at a Netto store on the Wrekin Retail Park.
The supermarket's trading director said it was a "bizarre" incident that was being taken very seriously.
Ms Willett, who was eating breakfast with her son at the time, said she first thought the snake was a free gift.
Describing the incident, she said: "My lad, he went to open his cereal and luckily enough I was behind him because a snake popped out.
"I just screamed. I grabbed the box off him and found some Sellotape."
She added: "Jordan's still in shock today. He's not eating. Neither am I."
The family, who bought the 89p packet of cereal on Saturday, said they would be taking things further.
Netto trading director Clive Cooper said: "This does seem to be a bizarre incident but we are taking it very seriously.
"Netto is in discussions with its supplier to ensure that all procedures are reviewed and we will be making checks on our stock."
An expert called in to examine the corn snake, which is non-venomous and feeds on mice and birds, said he was sure the animal had been kept as a pet in England and had been well looked after.