Contrary to popular belief, Tetanus isn't just the classic rusty nail, just as botulism doesn't only come in exploding cans. Tetanus thrives mainly in deep (usually dirty) wounds that have little or no access to the outside enviroment, such as puncture wounds and deep slash wounds. Rusty nails make unclean puncture wounds that the disease has no trouble getting into, but that's nowhere near the only cause. Any injury- even a pinprick- that's been contaminated by the enviroment can be an entering point for Clostridium tetani. However, most of the cases involve puncture wounds with local dirt or chemical contamination, thus the rusty nail cliché.