Woof!

Woof! was a British tv series, running from 1989 to 1997, about a boy who periodically changes in a dog, similar in premise to The Shaggy Dog.

The series begins with a Pilot Movie, about a kid named Eric Banks who suddenly finds himself occasionally turning into a small dog (naturally, usually at the worst possible times), totally at random, and naturally getting into all sorts of odd situations because of it. Throughout the movie he and his friend Roy try to find out what's causing it, and keep it a secret from Eric's parents, teachers, and everyone in between.

The show takes the concept and runs with it: featuring all sorts of wacky hijinks that a kid who randomly turns into a dog could get into. Hilarity Ensues. Later on, Roy moves away, and a girl named Rachel moves in instead who quickly discovers Eric's secret and takes Roy's place.

Further through the show's run, as the actors playing Eric and Rachel grew older, the focus changed to a new kid Rex Thomas, who inherits Eric's curse, and his best friend Michael, who take up the Secret Keeper role.

This series features examples of:

Animorphism
Catch Phrase: Roy - "Bril-ee-ant!"
Cloudcuckoolander: Roy, at times.
Empathic Shapeshifter: Of a sort. In the movie Eric and Roy come to the conclusion that his transformation happens because his sister wants a dog so much more than she wants a brother that it ends up making him actually change into one. In the end, it appears that they fix it, only for it to appear that it was Roy all along making Eric change, and not his sister. Later on in the show he is given a different explanation, however.
Evil-Detecting Dog: Doubles in that the dog is actually a kid all along.
Heroic Dog: Naturally. Also a plot point - at one point Eric tries looking for others who change like him by looking for news stories about dogs who are exceptionally smart and heroic.
Hidden in Plain Sight / Right Under Their Noses: When changed, Rex poses as his own dog, Bob, which fools everyone, including his father.
I Just Want to Be Normal: Eric, in stark contrast to his friend Roy who couldn't be happier about the whole thing.
Involuntary Shapeshifting: Pretty much the entire theme of the series.
My Instincts Are Showing / The Mind Is a Plaything of The Body: Eric and Rex are still themselves as dogs, but they are still dogs - they're fine with doing dog things that as boys they wouldn't want to do (like eating dog food) and instinctively do things a dog would do in situations (IE: Rex getting his father's slipper and the paper when he wants his attention, or rooting through trash when frustrated). As always, Hilarity Ensues.
Pilot Movie: Packed in a VHS, no less.
Prophetic Name / Punny Name: Rex, who has a name you're far more likely to see on a dog than a person. Ironically, when he changes he's called Bob, which isn't a name you usually find on a dog.
Secret Keeper: Roy and Rachel to Eric, Michael to Rex.
Suspiciously Similar Substitute: Rex and Michael to Eric and Roy, at least premise-wise.
You Meddling Kids: Occasionally