tony@w530 ~ $ cat bulk-index.txt 
{ "index" : { "_index": "test-index", "_type": "test-type", "_id": "1"} }
{ "foo": "b\ar" }
{ "index" : { "_index": "test-index", "_type": "test-type", "_id": "1"} }
{ "foo": "bar" }

tony@w530 ~ $ cat bulk-update.txt 
{ "update" : { "_index": "test-index", "_type": "test-type", "_id": "1"} }
{ "doc": {  "foo": "b\ar" }}
{ "update" : { "_index": "test-index", "_type": "test-type", "_id": "1"} }
{ "doc": {  "foo": "bar" }}

tony@w530 ~ $ curl -s -XPOST localhost:9200/_bulk?pretty --data-binary @bulk-index.txt
{
  "took" : 6,
  "errors" : true,
  "items" : [ {
    "index" : {
      "_index" : "test-index",
      "_type" : "test-type",
      "_id" : "1",
      "status" : 400,
      "error" : "MapperParsingException[failed to parse [foo]]; nested: JsonParseException[Unrecognized character escape 'a' (code 97)\n at [Source: [B@5ae957f1; line: 1, column: 14]]; "
    }
  }, {
    "index" : {
      "_index" : "test-index",
      "_type" : "test-type",
      "_id" : "1",
      "_version" : 4,
      "status" : 200
    }
  } ]
}

[2015-01-21 17:40:04,708][DEBUG][action.bulk              ] [nodeD2] [test-index][2] failed to execute bulk item (index) index {[test-index][test-type][1], source[{ "foo": "b\ar" }^M]}
org.elasticsearch.index.mapper.MapperParsingException: failed to parse [foo]
        at org.elasticsearch.index.mapper.core.AbstractFieldMapper.parse(AbstractFieldMapper.java:415)
        at org.elasticsearch.index.mapper.object.ObjectMapper.serializeValue(ObjectMapper.java:707)
        at org.elasticsearch.index.mapper.object.ObjectMapper.parse(ObjectMapper.java:500)
        at org.elasticsearch.index.mapper.DocumentMapper.parse(DocumentMapper.java:541)
        at org.elasticsearch.index.mapper.DocumentMapper.parse(DocumentMapper.java:490)
        at org.elasticsearch.index.shard.service.InternalIndexShard.prepareIndex(InternalIndexShard.java:413)
        at org.elasticsearch.action.bulk.TransportShardBulkAction.shardIndexOperation(TransportShardBulkAction.java:435)
        at org.elasticsearch.action.bulk.TransportShardBulkAction.shardOperationOnPrimary(TransportShardBulkAction.java:150)
        at org.elasticsearch.action.support.replication.TransportShardReplicationOperationAction$AsyncShardOperationAction.performOnPrimary(TransportShardReplicationOperationAction.java:511)
        at org.elasticsearch.action.support.replication.TransportShardReplicationOperationAction$AsyncShardOperationAction$1.run(TransportShardReplicationOperationAction.java:419)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
        at java.lang.Thread.run(Thread.java:745)
Caused by: org.elasticsearch.common.jackson.core.JsonParseException: Unrecognized character escape 'a' (code 97)
 at [Source: [B@5bcacee; line: 1, column: 14]
        at org.elasticsearch.common.jackson.core.JsonParser._constructError(JsonParser.java:1419)
        at org.elasticsearch.common.jackson.core.base.ParserMinimalBase._reportError(ParserMinimalBase.java:508)
        at org.elasticsearch.common.jackson.core.base.ParserMinimalBase._handleUnrecognizedCharacterEscape(ParserMinimalBase.java:485)
        at org.elasticsearch.common.jackson.core.json.UTF8StreamJsonParser._decodeEscaped(UTF8StreamJsonParser.java:2924)
        at org.elasticsearch.common.jackson.core.json.UTF8StreamJsonParser._finishString2(UTF8StreamJsonParser.java:2209)
        at org.elasticsearch.common.jackson.core.json.UTF8StreamJsonParser._finishString(UTF8StreamJsonParser.java:2165)
        at org.elasticsearch.common.jackson.core.json.UTF8StreamJsonParser.getText(UTF8StreamJsonParser.java:279)
        at org.elasticsearch.common.xcontent.json.JsonXContentParser.text(JsonXContentParser.java:86)
        at org.elasticsearch.common.xcontent.support.AbstractXContentParser.textOrNull(AbstractXContentParser.java:194)
        at org.elasticsearch.index.mapper.core.StringFieldMapper.parseCreateFieldForString(StringFieldMapper.java:337)
        at org.elasticsearch.index.mapper.core.StringFieldMapper.parseCreateField(StringFieldMapper.java:277)
        at org.elasticsearch.index.mapper.core.AbstractFieldMapper.parse(AbstractFieldMapper.java:405)
        ... 12 more

curl -s -XPOST localhost:9200/_bulk?pretty --data-binary @bulk-update.txt 
{
  "error" : "JsonParseException[Unrecognized character escape 'a' (code 97)\n at [Source: [B@cb1ae5d; line: 1, column: 24]]",
  "status" : 500
}