If you mean the difference between the two L’s in the word little, the first one [l] is the same as the Italian L of your acquaintance and is sometimes called a “bright L” or a “clear L”, while the second is an allophone of English sometimes referred to as a “dark L”, written [lˠ] or [ɫ].
The key difference is that the dark version is velarized, which here means that the back of your tongue flattens out and moves up a bit. The normal demo-word for this sound is FULL. If you have ever heard Catalan spoken, you will find that the Catalans often have dark L’s where a Castilian speaker would have a bright one like you do. It probably sounds a bit “swallowed” to your ear.
The exact distribution of these two allophones for phonemic /l/ varies by region, speaker, and syllable position. Some speakers have only one or the other of the two, while others have both. [reference]
Technically speaking, the dark L is:
The velarized alveolar lateral approximant, also known as dark l, is a type of consonantal sound used in some spoken languages. The regular symbol in the International Phonetic Alphabet that represents this sound is ⟨lˠ⟩, though the dedicated letter ⟨ɫ⟩ is perhaps more common.
In contrast, the other L is:
The alveolar lateral approximant, also known as clear l, is a type of consonantal sound used in some spoken languages. The symbol in the International Phonetic Alphabet that represents dental, alveolar, and postalveolar lateral approximants is ⟨l⟩, and the equivalent X-SAMPA symbol is l.
The expression is '... raining cats and dogs'. I have never heard of it raining dogs and cats.
But this is an expression, which a) is not meant to be taken literally and b) only holds when the 'cats and dogs' are taken as one (grouped) item
'... are as physically different as dogs and cats'.
In this sentence, the dogs and cats are not grouped, but are being referred to individually and separately. In addition, they are being referred to literally. In this context the phrase 'dogs and cats' is referring to two different four-legged, hairy mammals that people keep as pets.
The point the author is trying to make is that dolphins and porpoises (two very similar appearing animals) are actually quite different and that you should consider them as being as different to each other as much as you would consider dogs and cats as being different to each other. As @kojiro points out, in this context, the order of dogs and cats does not matter, yet as has been mentioned raining cats and dogs is always ordered cats, then dogs.
As an interesting aside, it seems other versions of it's raining ... for instance 'it's raining money', 'it's raining men', 'it's raining lawsuits', do refer to an abundance of the object - unlike raining cats and dogs - but the rain may be figurative. I suppose in that context - perhaps on entering an animal rescue shelter - you could say 'it's raining dogs and cats'.
Best Answer
I would say the third option:
As we see, towards means:
So the meaning should be: