The act of looking again at something out of surprise or disbelief; often used as 'to do a double take' (commonly used as 二度見する).
彼が隣の席に座っているのを見て、思わず二度見してしまった。
When I saw him sitting in the next seat, I couldn't help but do a double take.
あの看板は面白すぎて、通りすがりの人が皆二度見している。
That sign is so funny that passersby are all doing a double take.
彼女の髪色が変わっていて、思わず二度見した。
Her hair color had changed and I did a double take.