I'm currently smack dab in the middle of playing through Half-Life 2 Episode I, so seeing this hidden weapon makes me giddy. As soon as I defeat that mother ant-lion, I'm all over this crap.

Here's how you do it:

In console first type "hopwire_vortex 1" then "give weapon_hopwire" now throw it and then press attack again to activate it. It is preferable to do it in an area with lots of physics objects, I also suggest you stand back lest you wish to be crushed into singularity.

Very cool hidden stuff from Valve. Michael McWhertor

Something cool in episode 1