Cold email subject that got callbacks

I used “Quick help with your onboarding flow” as the subject and got 3 replies in 24 hours last Tuesday; inside was two sentences and a 40-second Loom showing a small fix I’d ship on day one. Anyone else sending micro-demos instead of cover letters, or want the exact blurb I used?

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I’ve had more callbacks with “35s teardown: [Feature] drops 12% at step 2” and a Loom plus a 4‑sec GIF preview in the email — think movie trailer, not the whole film… Caveat: some security blocks Loom, so I paste a one‑sentence fix under the link and offer an unlisted YouTube if needed — @OP do you personalize by product line or keep one generic micro‑demo per company?

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