I saw someone mention splicing...
Don't splice wires that are carrying 110 volt house current without using either solder, or the twisty-cap things. (twisty cap things are great, they're all over my house.) If the unsecured wires gradually pull apart, which they probably will, it could start a fire. I once saw an extension cord plug that had a loose/thin/bad connection in it explode when it was plugged in, leaving the plug in the wall socket and sending the cord a couple feet away from the wall (and leaving black marks on my fingers.)
Also, if they don't do that, when the wire connection starts getting thinner the wire can get red hot, melt the insulation, and burn stuff, if you've got a decent amount of current going through. (like a PC and some incandescent cab lights pull.)