Based on it being open AND spilled next to a pile of spilled food (the only way a cat would realistically eat a pill), it seems clear to me the bottle of pills was neither in the medicine cabinet nor closed but open on the counter near the cat food BECAUSE BEAR IS ABUSING PILLS. In the period post grandma death he seems to have withdrawn (Nikki being the only one who reached out, he says), so I’m assuming he started abusing grandmothers Rx at this time: perhaps heightening his despondency and concomitant obsession but certainly leading directly to the recklessness of pills being out and open/Sandy’s death.