You gave a mouse a cookie?
Would you like a little hysteria with your thread?
In my area, I’d worry about plague or hantavirus, especially with a non-house mouse.
Of course, no matter where you live, it would be more reasonable to worry about, say, getting struck by lightning than about getting any serious disease from your little friend.
Armed with mouse-like optimism, somehow I think he would have managed.
(Still, if you step on an invisible car in your bare feet at 3AM, you’ll have no one to blame but yourself.) 
Well, now I’m picturing him clutching his chest like John Hurt in ‘Alien’. Of course, I’m not quite sure what would burst out of a mouse’ chest…
[spoiler] …unless perhaps a stiletto heel from the other side?
Ladies, please don’t try this at home, because if you start going around with a mouse impaled on each heel, soon everyone will want one. Two even…
[/spoiler]
Well, it is NYC. I dare say you’re right…
Ah—the classic, time-honored reference text on the operant conditioning of mice… 
Or, he might just have eaten a low dose of rat poison, & it took all the piss & vinegar out of him.