sinker

n. (钓丝等的)锤,坠子

What I said was untrue but he fell for it/swallowed it(ie believed it) hook, line and sinker.

我所说的并非实话, 他却完全信以为真.

John was so easily fooled that he fell for Joe's story hook, line and sinker.

约翰是那么容易受骗，竟毫不怀疑地相信乔的话。