Calm Chain Chomp
From the Super Mario Wiki
Like other Calm enemies, C. Chain Chomp will usually be found asleep. Getting past one is tricky, because even the slightest sudden movement could wake the beast. Once awoken, it will attack like a normal Chain Chomp.
According to the game's Glossary, C. Chain Chomp is "Annoying if you wake it up. Jump quietly!"
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