I was cleaning out a chemical storage closet at work. A hydrogen chloride container leaked out onto some iodine containers. I picked one up (bare handed) and sat it down in the grass. About thirty seconds later, I noticed the steam boiling up from around the bottom of the container. This is about 45 seconds worth of contact.
I thought it was terrifying because this was a footprint of someone who was lurking around your house, looking through your windows.
And how long had they been standing there on one leg to cause the grass to grow around them?