Copy-Paste from Website to Terminal

You surely know this: You're looking at some website with some useful shell commands. However, those commands are long as hell and you know you're probably not gonna need them for a few years or so (so there's no need to memorize them). So, what do you do? You copy-paste them. Here's an example:

git clone/dev/null; clear; echo -n "Hello ";whoami|tr -d '\n';echo -e '!\nThat was a bad idea. Don'"'"'t copy code from websites you don'"'"'t trust!
Here'"'"'s the first line of your /etc/passwd: ';head -n1 /etc/passwd
git clone git://git.kernel.org/pub/scm/utils/kup/kup.git

Try running this command in your terminal. It's supposed to be harmless, right? It is harmless, yes, but what happens still isn't what you'd expect and demonstrates the dangers in doing stuff like that. Mark it with your mouse, copy it somehow (e.g. using CTRL+C) and paste it into a terminal. What happens?