diff --git a/src/fib/fiber.ml b/src/fib/fiber.ml
index 25a4485e..7ddb294b 100644
--- a/src/fib/fiber.ml
+++ b/src/fib/fiber.ml
@@ -149,6 +149,7 @@ let k_current_fiber : any option Task_local_storage.key =
   Task_local_storage.new_key ~init:(fun () -> None) ()
 
 let spawn_ ?name ~on (f : _ -> 'a) : 'a t =
+  Printf.printf "spawn fiber\n%!";
   let id = Handle.generate_fresh () in
   let res, _promise = Fut.make ?name () in
   let fib =
@@ -162,8 +163,10 @@ let spawn_ ?name ~on (f : _ -> 'a) : 'a t =
 
   let run () =
     (* make sure the fiber is accessible from inside itself *)
+    Printf.printf "run fiber 0\n%!";
     Task_local_storage.set k_current_fiber (Some (Any fib));
     try
+      Printf.printf "run fiber\n%!";
       let res = f () in
       resolve_ok_ fib res
     with exn ->
diff --git a/src/unix/ev_loop.ml b/src/unix/ev_loop.ml
index 8c25fea5..64286281 100644
--- a/src/unix/ev_loop.ml
+++ b/src/unix/ev_loop.ml
@@ -202,14 +202,18 @@ module Ev_loop = struct
 
     let delay = run_timer_ self.timer in
     let delay = Option.value delay ~default:10. in
+    Printf.printf "delay: %f\n%!" delay;
 
     (* run [select] *)
     let reads, writes = IO_tbl.prepare_select self.io_tbl in
     A.set self.in_blocking_section true;
+    Printf.printf "ENTER (%d read, %d write)\n%!" (List.length reads)
+      (List.length writes);
     let reads, writes, _ =
       let@ _sp = Tracing_.with_span "moonpool-unix.select" in
       Unix.select (self.pipe_read :: reads) writes [] delay
     in
+    Printf.printf "EXIT\n%!";
     A.set self.in_blocking_section false;
 
     drain_pipe_ self;