Depends which

its obviously, well, ummm, more? i think

Of course it depends of which one is it. Not every poisonous "thing" acts the same way.

Less. If it was more it wouldn't be expired.

Won't know until you try it!

Let's find out shall we!

Less. Work on a farm, and if you use an expired poison for weeds/insecticide you can expect them to stay around. It means the active constituent (part that kills) has broken down, and won't work to its' full extent.

I didn't know that poisons can expire

The poison will act slower, but it will eventually work. It causes stomach cancer as the chemicals slowly eat away at you. This is what happened to Napoleon.