Brock tears into it with an almost sexual fervor, spraying blood across his face and green vest.

"That's funny, I think a murder may have occurred in or around this bag!" Brock says, ignoring the screams.
He pulls out the small intestines first, and then the large. He gives it a lick and then a sniff - probably the reverse order of what he should have done.

The screaming intensifies. Behind him, Bulbasaur is using vinewhip on and inside a dirty little vulpix. The vulpix is crying, but it hasn't said the safeword yet, so Brock hasn't called any of this off.
It hasn't occurred to Brock that the vulpix cannot speak Japanese, and therefore cannot say the safeword. The safeword is more of a safety phrase, and it goes along the lines of "Brock, pay attention this time, so that Meowth won't die in vain! You made Meowth's safeword 'Meowth!', which he repeated ad nauseam while begging for his life! You didn't listen~! YOU DIDN'T LISTEN~!"
But all the vulpix kept repeating was "Vulpix! Vulpix!"

Brock thought that was super sexual as he started yanking bones from their ligaments. This was all being filmed.
He had gotten off light, last time. He was sure he'd get off light again.
The screaming turns into gurgling, the gurgling turns into a death rattle, and the death rattle is echoed by another death rattle, that of the vulpix, which the Bulbasaur keeps incessantly beating.

What's in the garbage bag? It's blood and bones and other various instances of organic trash.

It doesn't occur to Brock that it's not a garbage bag at all. It's Clefairy~!