[Rainclouds]

These are all experts.

SB checked the river because he knew BB had nothing, and BB would bet. MP would call the bet with his boat (not raise, only quads would call a raise obv) and SB could then CRAI. SB knew all this.

BB knew that of SB's plan, concluded that SB had obvious quads and wisely checked the river.

MP knew that SB checked the river because SB knew that BB had nothing and would bluff so that he had to call and SB would CRAI. The fact that BB checked here is being results orientated. BB's check still means that SB has quads and MP picked up on this.

These players could be crushing 300/600