Which decisions can the on-field umpires send to the third umpire themselves?

These are umpire reviews. They don't use up a team's reviews, and players aren't allowed to appeal for one (doing so can be treated as dissent).

The on-field umpires can refer or consult on:

• Run out, stumped, bowled and hit wicket appeals (the umpire draws a TV-screen shape)
• Catches and bump balls, and obstructing the field, after the two on-field umpires have consulted each other
• Boundaries: whether it's a four or a six, whether a fielder touching the ball was touching or grounded beyond the boundary, and runs from a boundary overthrow. If the evidence is inconclusive, no boundary is given.
• Which batter made their ground first when both run to the same end
• Short runs: the third umpire automatically reviews every short-run call
• No balls after a dismissal, other than the front foot, which is already checked every ball
• Ball hitting an overhead camera (spidercam) or its cables

The third umpire can also contact the on-field umpires on their own initiative about a missed boundary infringement or the ball hitting an overhead camera.

The third umpire shows the decision with a red light (out) or green light (not out), or on the big screen.