Coffee and slugs?

We were watching a gardening show of some sort this evening when our interest was piqued by a method of killing slugs and snails that I had never heard of.

This piqued my interest because we get a slug in the kitchen almost every night. I just disposed of one longer than my thumb. We sometimes get some that are as long as my thumb and forefinger outstretched.

So I am always open to new ways of nuking them.

The gardening show suggested making up a cup of espresso coffee, diluting it with 5 parts water and then pouring it around any plants that are getting chomped.

Coffee?

How on earth does coffee kill slugs?

Does it speed them up and make them go so fast that they get ahead of their slime trail, and thus die of dehydration? What's the story here?

I tried a shortcut tonight by simply pouring a few instant coffee granules onto a captured slug. Apart from a bit of wriggling, not much death seemed to be stalking slugland. I wanted to spend some time on slugdeathwatch, but J was not too happy with the thought of me leaving a writhing slug on the kitchen bench, so the experiment was terminated early.

Thus is scientific progress impeded.