Our cats spend most of their time lazying about, eating, playing, sleeping (a lot) and yawning (a lot, too). I love taking photos of them with their mouths open when they're doing the latter. And since they do it pretty often, it's not so hard to snap them right that moment, hehe.
Warning: some of them are really creepy.
Oh, boy! I totally feel like yawning now, hehe :p.