The speaker has just watched a circus show and can't quite believe it, even though they saw it with their own eyes. Speaking to a friend, they say "It's impossible!" and the poem keeps circling between amazement and suspicion.
The animals seem to do "unnatural things," as if they've turned into people, though the speaker shrugs that a beast will do anything for sugar or fish. That bracket is wry and a little cynical: the magic is really a bargain. The acrobat is godlike, but the clown, who is also trainer, trumpeter and acrobat, seems to be everything at once, as if the whole show is one performer in different costumes.
The ending is the most unsettling part. The musicians are barely visible, and the speaker wonders whether the music is just a tape in a locked van. The mood is playful but uneasy: delight in the spectacle, mixed with the nagging sense that the illusion hides a trick.