One point makes the T live
The T-four is a straight three grown one stub: four points of eye space with a single centre point where every arm meets. As with every undecided shape, that junction belongs to whoever takes it first — yours, and the space bursts into eyes at once; White's, and the group is one eye and a capture fight. The wrong move is any point at the end of an arm, which leaves the junction untouched. Black to play: make two eyes in the T-four.