Mica Craig from Clarkson, Washington, is recovering after he was bitten by a rattlesnake in a garden department of Wal-Mart.
Mica Craig, 47, said the reptile pounced as he was shopping at Wal-Mart in the north-western US state of Washington.
The man stamped on the serpent and was later treated at hospital with anti-venom, after his hand suffered serious swelling.
Wal-Mart apologized, and said it was investigating how the snake had entered the store in the city of Clarkston.
Kayla Whaling, a spokeswoman for the chain, said: “At this point, it appears to be an isolated incident.
“We are working with a pest management team, which is conducting a sweep of the property to ensure there is no additional rattlesnake activity.”
Another customer, Maria Geffre, told Reuters news agency the snake was at least 1 ft (30 cm) long with four rattles.
Mica Craig said the serpent attacked as he reached down to brush away what he thought was a stick from a bag of mulch.
The purchase was intended for his marijuana plants, which Mica Craig said he was licensed to grow for medical reasons.