What it looks like
A threat posture commonly involves the front legs being raised, sometimes with the fangs visible. It is a clear signal that the spider feels pressured and wants distance.
Do not test it
Do not poke the spider to see whether it will strike. The correct response is to reduce pressure and give it a route back to the retreat.
Why it happens
Cornering, vibration, enclosure maintenance and failed rehousing attempts can all trigger defensive displays. Old World species may rely on this behaviour more because they lack abdominal urticating hairs.
Feeding response is different
A feeding strike can be fast and direct without a prolonged raised posture. Learn the context rather than assuming every sudden movement is aggression.
Change the maintenance plan
If routine tasks repeatedly provoke threat postures, improve access, use longer tools or adjust the enclosure layout so the spider does not need to be crowded.
Respect without fear
A threat posture is useful communication. Backing off makes the interaction safer and usually lets the spider settle quickly.