Then lets say you packaged that up as a library. Another guy did the same thing, but it worked a little different. Now random code breaks.
And on the "technically, could it happen?" side, sure, it could. You can also write a Java library that, in weird cases, could screw up other Java libraries, but the Java folks (even as much as they love to try to keep you safe) don't care, either.
Besides, "each" is quite standard in Ruby. Defining it to mean something other than "call the proc with each element, in order" would be weirdbad, like a C++ programmer defining operator+ to mean subtraction. If you do something weirdbad like that, your library deserves to lose.