They were confabulating at the cafe for the whole afternoon.

confabulating 是动词 confabulate 的现在分词形式。confabulate 由前缀 con-（表示"一起"）和拉丁词根 fabulari（意为"谈话"）组成，字面意思是"一起谈话"，引申为"闲聊、闲谈"的意思。