It takes a little detective work to suss out the form of this poem, especially when the line lengths in stanza 2 vary so much. A good way to start thinking about form is to look at the shape of the stanzas.
Here we have four-line stanzas, a common type of stanza called a quatrain. Quatrains are especially popular in rhymed poetry, so let's look for end rhymes (the rhyming words at the end of lines, just like it sounds).
Hmm… There don't seem to be any exact end rhymes in the first stanza, but "moaning" and "drowning" both share an "n" sound before the matching "-ing" endings. We call that a feminine rhyme. So, this stanza sort of rhymes ABCB. What about the other stanzas? Same thing, though stanza 2 uses exact end rhymes: "dead" and "said."
Quatrains with an ABCB rhyme scheme already give us enough information to make a pretty good guess at the poem's form, but let's take a look at the meter, too, just to be sure.
Focus on the stressed syllables. This is how Shmoop hears the first two lines: "Nobody heard him the dead man, / but still he lay moaning." The first line has four stresses, and the second has three. You'll find that lines 3-4 repeat this alternation of four and three.
Each stress is part of a metrical unit called a foot, which usually consists of one unstressed and one stressed syllable. Four feet in a line is called tetrameter (tetra- means four) and three feet in a line is trimeter (tri- means three). So in the first quatrain, we have alternating tetrameter and trimeter lines.
Okay, now we're really getting somewhere. We know the first stanza is a quatrain with alternating tetrameter and trimeter lines rhymed ABCB. This happens to fit the definition of ballad stanza, a popular verse form used in songs and closely related to the form of religious hymns. Usually a ballad tells a story, but its form can be used for many purposes.
As you can guess, though, this simple description of the poem's form isn't all there is to say. For one thing, it doesn't detail the kinds of metrical feet that occur in the poem.
The most common foot in English poetry is the iamb, which is an unstressed syllable followed by a stressed syllable. The first two feet of the second line are iambic: "But still he lay." Hear that daDUM daDUM?
In fact, the iamb is the most frequently used foot in the poem, but that's not to say the poet is making things easy for us. Look again at how wacky that first line is: "Nobody heard him the dead man." Sure, the second foot is an iamb, but what's going on with the rest? Well, the first foot starts with a stressed and then an unstressed syllable. This is the reverse of an iamb, also known as a trochee. Smith likes to sprinkle trochees all over the place to give a little variety to the verse so it doesn't just thump along like daDUM daDUM daDUM daDUM for 12 lines.
You might also notice that Shmoop hears the last two feet in line 1 as two unstressed syllables followed by two stressed syllables. The terms for these feet are pyrrhic and spondee, respectively. Some professional metrists (yes, that's a real occupation) argue that these two feet don't exist or are very rare in English; others say that it's fairly common to see a relatively unstressed foot followed by a foot with two heavy stresses. Yes, this is actually a thing that people argue about. Don't stress out about it. (See what we did there?) It's enough to know that the poet has some interesting metrical tricks up her sleeve to keep things from getting boring.
In general, you could say the poem is roughly in ballad meter (alternating lines of tetrameter and trimeter) and is mostly iambic with frequent trochaic substitutions (just a fancy way of stating that the trochees don't outnumber the iambs). Go ahead, say it and impress your friends.
Why do we say the poem is "roughly" this way? Because there are some exceptions. Of course. If you glance at stanza 2, you'll see that lines 6 and 8 are too short and line 7 is too long. Like, way long, as if it stole a couple feet from the lines around it. This forces you to make a decision when you're reading the poem out loud: do you pause longer after the short lines and speed up on the long one, or do you read at a normal pace and make it sound like the long line is giving its syllables back to the shorter lines?
Try it out and see what feels most comfortable, then listen to Stevie Smith read it herself. What are the different effects of these lines when you read them on the page compared with when you read them out loud? We're not quite sure why she makes these lines so irregular, but we think she's having fun with the reader and making us take a more active role in how we process her poem by speeding up and slowing down when the occasion calls for it.