Do animals grieve?

In the weeks since Marley’s death, Biscuit has been acting differently. Before, he would spend most of the day huddled quietly somewhere, but now, he paces around the house, meowing and meowing incessantly (oddly enough, just like Marley used to do). He’s much needier now, too, and actively seeks out affection from Melissa. He even rolls over on his back and lets her scratch him. This is something he never used to do.

Biscuit’s change in behavior has made us wonder if he’s sad or freaked out about Marley. Does he know what happened to him? Is that why he was howling when Marley died? When he wanders around the house now, is he looking for his brother?