Intended audience: Intermediate and up

Neither vul, matchpoints:

North: ♠AJ763 ♥Q ♦AK4 ♣K763

South: ♠Q95 ♥A98 ♦Q10743 ♣AJ

Their auction:

¹ 12-14

² Transfer

³ Acceptance (super-accepts not played)

⁴ At least 5-4 in the blacks, slam try

⁵ Confirming 3+ spades, non-minimum

⁶ Cue bid

⁷ Non-forcing

⁸ Nothing more to say

Who is to blame for missing slam?