Not sure if anone noticed it, but there is no information about big tentacles in DST.
Basically, what I've seen is that they won't drop any item, nor cause an earthquake. Instead they just retreat and let you travel through the hole they've been in. It works kinda like wormhole, it spits you out next to another big tentacle.
However, I'm not sure if the travel costs you anything, like sanity, if they are paired up, if the tentacles ever come out again and more.
If you have some information about these "cave wormholes", please share it on the Big Tentacle page. I, as well as other hungry cave dwellers, would appreciate your help.
sry4eng ;)