A lovely Giardia cyst.
This army will then position itself, creating a blanket on the brush border of your intestine, effectively shutting down absorption of fats, proteins and other nutrients and causing a lovely, foul smelling diarrhea. This smell is brought to you courtesy compounds like cadaverine and putresine. Interestingly enough, the product Olestra causes similar symptoms.
But, despite all this, the coolest thing about Giardia is what the trophozoites look like once hatched from the cyst:
Cute, eh? The smiling face eyes are actually from the nucleus and the nucleolus, the mouth is from the median bodies, its' cute "hair" is from its' flagella and its' nose is actually part of the outline of its' ventral sucker. By the way, the "line" down its' face is its' axostyle! And, for sheer awesomeness...
Anddd... its' attempt to be The Sorting Hat....
For more info, I give you - Giardia The Wiki
So, there. Now you all can love Giardia as much as I do!
EDIT: I forgot to add how you can tell if you have Giardia - besides the presence of severe abdominal pain. When doing a fecal test it's actually really difficult to determine whether you have it, despite its' characteristic shape. This is because Giardia is shed intermittently so you could actually have the parasite and not know it and wind up shedding it everywhere. In the veterinary world, the best diagnostic tool is using an antigen test. Also, there is a vaccine out there for dogs but it doesn't work very well, even with boosters as there are so many regional strains of it and immunity wanes... Unfortunately, I don't know about human medicine! haha.