In general, the scientific community seems to believe that only the so-called "higher" animals, like cats, dogs and even rodents, are capable of any notable level of intelligence. However,. to people who pay attention, startling displays of intellect may be seen in the "lower" animals, as well. Animals like slugs.
I keep all of my adult and semi-adult slugs and snails in a bin separate from the babies. The lid of this bin has presented something of a problem for a while now. The latches on either side were constructed in such a way that the slugs could crawl through the hinge holes on the lid's underside and escape through a small gap between the latch and lid. They didn't do this at first, but then one slug did it, and soon enough many of them were doing it every night.
So I popped the latches off and sealed up the holes. I didn't need them on there, anyway. I figured that was the end of their escapades. I was wrong.
A little under a week later, after the lights had been turned off for the night, I go to check on them as I always do and I notice a lone slug sliming his merry way down the outside of the bin! I couldn't figure out where he had come from. I though that he surely couldn't have gotten out. I scooped him up and put him back into the bin, brushing the incident off as a freak accident. I thought that he might have gotten out when I'd had the bin open earlier that day and stowed away underneath the lip of it for a nap. It's happened before.
I'd forgotten the incident entirely until the next night. I'd turned out the lights for the night and was going to feed them and do some slug-and-snail watching. I was stunned to see not one, but four slugs had mysteriously appeared on the outside of the bin and on top of the lid! I was baffled as to how they could have been getting out. Fortunately, a fifth slug was in the process of revealing their secret. He was squeezing himself through the tiniest little gap that existed between the lid and the bin, right where the latch would have fastened them together. As soon as he noticed I was there, he started going back in. Since then, I've been taping up these gaps each night before I go to bed so they don't get out.
The thing I noticed first about these incidents was that it started with one slug one night and many the next. It makes me feel convinced that there must be some sort of communication going on between them. Like one slug is reporting to the others that he found a breach and was able to get out. Another thing I noticed was that they seem to be capable of remembering the locations of the breaches. I also imagine that when they noticed the first path had been eliminated, that they set to work searching for another. The tiny gap between lid and bin was too small to have been found on accident. It makes me wonder if they go around testing for weaknesses, and if so, something like that could very well point to problem-solving abilities.