Don't mention legal concepts or buzzwords you do not feel comfortable explaining. From my personal experience, if you mention a specific legal principle or a buzzword then you could very likely be asked to explain it/provide a definition.
If you are unsure or unclear about what they are asking you, you could ask them to phrase it another way. I would then attempt to give an answer. If you are incorrect or not on the right track, they will try to guide you towards the right answer. This is from personal experience at assessment centres and at HSF specifically.
They are not trying to catch you out, they just want to see how your mind works and how well you deal with challenging situations.
If you are challenged/pressed, it is important to remain calm and not show your nerves. Thinking out loud while trying to come to a solution is a good idea instead of shutting down and getting flustered.
I had an assessment centre at HSF for a VS and was successful. There were times I did not understand some of the words/concepts the partners were using and they were more than happy to explain further until I got it.
Just approach each station as if you were having a normal conversation. That helped calm my nerves before AC's in the past. Come in with confidence from the beginning. Even if one station did not go so well, it is important to remain calm, confident and level-headed.
HSF are genuinely a really nice and friendly firm. All the best.