made this up on holiday:
this psychology student is running an experiment, right, and she wants to measure the base rate of human error, so she picks a ludricously easy task, and montiors how succesfully volunteers perform at it; she decides to take a pair of chimes and just 'ting!' them together, different numbers of times, and the volunteer must say how many times they hear the sound. so she has lots of volunteers, and gets some good data.
on the last day of the experiment, a stereotypical irish man walks in. she explains the experiment to him again, saying, "all you've got to do is say how many times i've rang the chimes," he says, "okay, okay." so she rings the chimes once - 'ting!' - and the man says, in his best gruff irish accent, "one," and then she rings it several times, and the man pauses a moment and says, "that would be a river-dwelling mammal."
the experimenteer is silent for a beat; then explodes.
"What!? why the hell did you say that? what's that got to do with anything?"
the irish man relaxes back in his chair, takes a wee dram from a previously unobserved bottle of Power's, and says...
"well, you see, with me, it's either one t'ing or an otter!"