दंष्ट्राकरालानि च ते मुखानि दृष्ट्वैव कालानलसन्निभानि। दिशो न जाने न लभे च शर्म प्रसीद देवेश जगन्निवास ॥

danṣhṭrā-karālāni cha te mukhāni dṛiṣhṭvaiva kālānala-sannibhāni diśho na jāne na labhe cha śharma prasīda deveśha jagan-nivāsa

Like Time's destroying flames I see Thy teeth, Upstanding, spread within expanded jaws; Nought know I anywhere, no shelter find; Mercy, O God! refuge of all the worlds!

In plain words: Arjuna sees Krishna's teeth like the fires that destroy the world at the end of time. He is so lost he no longer knows which way is which and finds nowhere to feel safe. He begs Krishna for mercy, the shelter of all the worlds.