In our case:

over there; bed; basket; lead; walk; wait at the door; go to [room]; go to [family member]; stay; stay on the path; paw; paws up; sit; lie down; heel; don't pull on the lead; no more poo poo; no more wee wee; this is the commute; up; where's your piggy?; treat?; buscuit?: up for a cuddle?; want to come up?; permission; okay; no; stop; this way; stay close; hungry for some food?; water?; down; don't lick; who did this?; come here; shall we go the pub; let's go;

and probably 5 or 6 more words/phrases. I don't include words like catch/fetch where accompanying action may trigger the response.

It's definitely not a three year old's grasp of language, but it's probably a point that a baby crosses somewhere between 9 and 15 months old.