Not only Song Yun, but any mercenary who has been on the battlefield would have a habit.
When facing any action or behavior that could potentially threaten themselves, the first instinct is to kill the opponent!
Song Yun is a very professional mercenary.
Therefore, when faced with the Browning Beast Eyes aimed at his neck, even though the dagger wasn't sharpened and Wen Ting's strength was negligible, Song Yun instinctively reacted with a counterattack.
And Song Yun's method of counterattack is to stab.
Holding the dagger in his hand, he stabbed at Wen Ting's heart.
Here's an explanation of why the stab was aimed at Wen Ting's heart and not somewhere else like the neck.
