Hi there. It was explained to me that Canines are so fast because they have four legs so run horizontally, not as an erection. When playing some humans (myself included) crawl on all-fours. This seems silly now, although I'll still do it because I love dogs (and also most animals.) All except Spiders! Eight-legged freaks. Just don't let your dog lick your mouth until you've brushed their teeth! Four legs? Probably been stamping on someone's head. ☺