The International Festival of One-Liner jokes

I got this one is the mail this morning:
One guy says to the other: I am dating 2 anorexics, 2 birds 1 stone!!
I didn’t get it at first, having not lived in the UK for about 30 years, I had forgotten that a stone is an obscure British measure of weight. It didn’t help that I thought anorexics were people who had lost their memory.
Sometimes we can all be really thick.