Why does st bartholomew carry a knife around?

St. Bartholomew does not carry a knife around. He is depicted holding a knife due to the manner of his death, rather than a symbol associated with life.

Saint Bartholomew is one of the Twelve Apostles of Jesus. According to Christian tradition, he was martyred in Armenia, where he was flayed alive and then beheaded around 68 AD. As such, he is often depicted in art holding a knife, the instrument of his martyrdom.