Having a laugh

It's commonly held that people with autism lack a sense of humour. Specifically, they struggle to understand jokes other than the most basic ones. No less a person than Hans Asperger declared that people with autism "never achieve that particular wisdom and deep intuitive understanding that underlie genuine humour" (translation courtesy of Uta Frith). Then again, you might say, he was Austrian, so what would he know?
Less flippantly, I have to ask: if autism is a humour-free condition, why does Euan spend so much time laughing? In fact, I'd go so far as to say that visual jokes are one of his strongest means of communication. He'll think of something funny, act it out, and look up for our response. The difficulty is understanding what's going on in his mind. When he shares a joke, is he really sharing, or just performing?
Euan's stock in trade is incongruity. There's a section of my Facebook page called My Children's Idea of Art which is filled with impromptu sculptures. Two plant pots with skippy balls sticking out of them; toy cars arranged among fruit in a bowl (actually, some of these are his brother's, but that's another issue...). On the flight to Germany he decided that the little tog that holds the flip-down table up against the seat in front of him was a tap, and spent most of the flight pretending to pour drinks into a cup, accompanying the action with gurgles of delight. He loves to take an object and put it somewhere it doesn't belong: stick-shaped crisps in a drinking cup being a recent example. When he does combine objects that belong together, it's in an incongruent way, such as the time he lined up four plastic buckets, filled them with sand, then planted a spade squarely in the centre of each bucket as if it were a tree.
Euan's sense of humour is idiosyncratic. Perhaps it's a way of subverting his own love of order and routine - if he can control the disorder, he can laugh at it. It may also be why he laughs like a drain whenever he sees someone stub their toe and wince - not out of cruelty, but at the sheer incongruity of seeing a soft toe combine with a hard skirting board, and the extreme contortion of the victim's face that results. Odd facial expressions are another thing that amuses Euan, which is partly why it's so hard to tell him off. The more the rage registers in your face, the greater his delight.
It still leaves the question of whether he does, or can, interact through jokes. I have a sense that it might be a way to connect with him. Verbal jokes are still beyond him, but the evident joy he takes in inventing, sharing and - more rarely - getting jokes contain some encouraging signs. When he looks to someone's face to see if they're laughing, and laughs even harder in response, it's a kind of communication. The next step is regulating it, which means teaching him, among other things, that stubbed toes aren't always funny. But mostly they are.