Hobbs (Peter Madden) was always shown holding a knife.
The first episode broadcast in the United States ("Battle of the Cameras") actually features two opening credit sequences. The first is a brief, 10-second introduction featuring a few bars of "Secret Agent Man" and a credit for Patrick McGoohan (running roughly the same length as the original UK credits). This is followed by the teaser, and then the regular credits. In all future US broadcasts, the pre-teaser credit sequence was dropped.
Besides the theme song, other changes were made to the credits between the UK and US versions. In the UK version each episode starts with a very brief opening credits sequence introducing Patrick McGoohan. The teaser follows, and then after the commercial break the rest of the theme (High Wire) is heard as episode credits roll. The US version eliminates pre-teaser credits (except in the very first episode), inserting the "Secret Agent Man" credits after the teaser in the usual location (for US programs).