What does it mean when a dog licks another dog under the chin?

I'm taking care of some family's dogs for the week, but I only own one dog. My dog always seems very aggressive towards other dogs, but they seem to be getting along alright. My dog is always trying to lick under the chin of one of the other dogs, and that dog doesn't seem to like it much. Is that some type of communication, and if yes, what does it mean?

Also...since I've got you here :) ... my dog keeps taking the toys aways from that particular dog. If the one dog starts playing by himself with a toy, or if they start a game of tug of war, my dog starts growling and takes the toy away. Is that how dogs normally play, or is my dog being a bit selfish?

Licking the face/mouth is submission to the other dog, most domimate dogs don't like it much and will growl and show agression. its what puppies do to mom wolves to invoke... hmm well feeding.... it makes them up chuck food for the pups. older dogs who do this to an alpha is corrected by a growl or just a show of teeth. it also mean ur dog is a bit insecure.

note how the other dog is standing his chest out, head high, tail up. he's holding his ground, this is a dog that starts a fight with others that want to fight. but ur dog is saying i want to be friends....u are boss. i would correct the aggresser. a light touch on the shoulder or neck. and be sure the dog walks away not u.

taking toys is a normal play at my house, it involes growling and barking...and running around like crazy dogs they chase and play tug o war. but i stop play when it goes beyond playing to being slightly aggressive. i can hear the change of tone in the dogs... a growl deepens to a snarl...and a bark changes to that deep growlish bark. that is like when someone is at the door. they stand differ..like i said above....their brother and have been together their whole lives.

but i can't see if ur dogs are playing..or if they mean business.

Obviously the Dog is either stressed or the dog is jealous of the other dog. : ) http://answers.yahoo.com/question/accuse_write?qid=20070719092805AAVkuky&kid=NYxUWnLgBG0iVd744U0t&s=comm&date=2009-05-04+16%3A00%3A01&.crumb=

the dog might like other dog http://answers.yahoo.com/question/accuse_write?qid=20070719092805AAVkuky&kid=A8ZmPlbKV3a48EkFQp4T&s=comm&date=2009-07-30+14%3A02%3A54&.crumb=

All together he is just showing affection either that or the other dog has food on his chin. All dogs play tug of war that way they are like kids if one plays with a toy the other will try to take it away.

Simple, your dog is jealous. He is also showing submission to the other dog, meaning that the other dog is more dominate, which is the licking under the chin. It is complety normal, just like your dog licking your face. He is letting you know that he knows you are the boss and is not trying to take it from you.